Skip to main content

Full text of "The social life of animals"

See other formats


THE  SOCIAL  LIFE  OF  ANIMALS 


THE 

SOCIAL 

LIFE 

OF  ANIMALS 

BY  W.  C.  ALLEE 

PROFESSOR  OF  ZOOLOGY 
THE  UNIVERSITY  OF  CHICAGO 


WW-  NORTON  &  COMPANY  •  INC 

Publishers,  New  York 


Copyright,  1938,  by 
W.  W.  Norton  &  Company,  Inc. 
70  Fifth  Avenue,  New  York  City 


First  Edition 


Published  by  arrangement  with 
The  University  of  Chicago  Press 


printed  in  the  united  states  of  AMERICA 


This  hook  is  gratefully  dedicated  to  the  past  and  present 
members  of  our  "Ecology  Group";  without  their  enthusi- 
astic co-operation  much  of  the  underlying  evidence  could 
not  have  been  collected  during  my  lifetime,  and  without 
their  critical  attention  the  expression  of  these  ideas 
would  have  been  more  faulty. 


Contents 

Foreword  13 

I.  Science  versus  Metaphysics  15 

II.  History  and  Natural  History  20 

III.  Beginnings  of  Co-operation  50 

IV.  Aggregations  of  Higher  Animals  90 
V.  Group  Behavior  133 

VI.  Group  Organization  175 

VII.  Some  Human  Implications  209 

VIII.  Social  Transitions  244 

Literature  Cited  277 

Index  289 

52556 


Illustrations 

PLATES 

FACING  PAGE 

I  A.  A  hibernating  aggregation  of  ladybird  beetles  32 

I B.  A  breeding  aggregation  of  midges  32 

II.  A  grassland-bison  community  38 

III.  Aggregating  behavior  of  brittle  starfish  44 

IV.  Diagrams  showing  the  effect  of  population  size 

on  the  rate  of  evolution  128 

V.  Castes  of  a  termite  from  British  Guiana  266 

FIGURES 

PAGE 

1.  Grasshopper  nymphs  on  the  march  36 

2.  The  effect  of  numbers  present  on  rate  of  bio- 

logical processes  52 

3.  Group   protection  from   ultra-violet   radiation 

for  planarian  worms  60 

4.  Another  aspect  of  group  protection  for  plana- 

rians  62 

5.  The  small  marine  flatworm  Procerodes  64 

6.  Group  protection  from  fresh  water  for  Proce- 

rodes 66 

7.  Bacteria  frequently  do  not  grow  if  inoculated 

in  small  numbers  67 

8.  The  common  sea-urchin  Arbacia  70 

9.  Arbacia    eggs    cleave   more    rapidly    in    dense 

populations  72 

10.  Robertson  found  that  two  protozoans  placed 

together  divided  faster  than  if  isolated  76 

9 


lO  ILLUSTRATIONS 

PAGE 

11.  Other  protozoa  reproduce  more  rapidly  when  a 

certain  number  of  bacteria  are  present  78 

12.  Some  protozoans  divide  more  rapidly  in  dense 

bacterial   suspensions  if  more   than  one   is 
present  79 

13.  A  and  B.  A  recent  suggestion  concerning  the 

ancestral  relations  within  the  animal  king- 
dom 86 

14.  Goldfish  grow  more  rapidly  if  placed  in  slightly 

contaminated  water  95 

15.  An  extract  from  the  skin  of  goldfish  frequently 

has  growth-promoting  power  97 

16.  White  mice  grow  faster  in  small  groups  than  in 

large  ones  101 

17.  Flour  beetles  reproduce  more  rapidly  if  more 

than  one  pair  is  present  105 

18.  The  "spread"  of  time  in  which  eggs  are  laid  in 

a  colony   of  herring   gulls   affects   the   per- 
centage that  survive  ii2 

19.  In  small  populations,  genes  drift  into  fixation 

or  loss  largely  irrespective  of  selection  121 

20.  In  medium  populations  complete  fixation  or 

loss  is  less  likely  to  occur  123 

21.  In  large  populations,  gene  frequency  is  held  to 

a  certain  equilibrium  value  by  the  opposing 
pressures  of  mutation  and  selection  124 

22.  As  intensity  of  selection  increases  it  becomes 

more  and  more  dominant  in  determining  the 
end  result  126 

23.  Manakin  males  establish  rows  of  mating  courts 

in  the  Panamanian  rain-forest  134 

24.  Many  kinds  of  fishes  eat  more  if  several  are 

present  136 


ILLUSTRATIONS  1  1 

PAGE 

25.  An  ant  which  works  at  an  intermediate  rate 

may  be  speeded  up  if  placed  with  an  ant 
which  works  more  rapidly,  or  vice  versa  141 

26.  A  simple  maze  used  in  training  cockroaches  151 

27.  Isolated  cockroaches  make  fewer  errors  during 

training  than  if  paired  or  if  three  are  trained 
together  152 

28.  They  also  take  less  time  153 

29.  Parrakeets  learn  equally  well  if  trained  when 

isolated,  whether  they  are  caged  singly  or  in 
pairs  156 

30.  Parrakeets  learn  more  rapidly  if  trained  alone 

than  if  two  are  placed  together  in  the  maze     157 

31.  Feeding  a  fish  which  has  just  come  through  the 

opening  from  the  larger  side  of  the  aquarium     160 

32.  Goldfish  learn  to  swim  a  simple  aquarium-maze 

the   more   readily   the   more   fish    there   are 
present  161 

33.  Isolated  goldfish  learn  the  problem  set  for  them 

less  rapidly,  and  unlearn  it  more  readily  162 

34.  The  aquarium-maze  used  in  training  part  of 

the  fish  to  come  forward  and  part  to  go  to  the 
rear  to  be  fed  164 

35.  Cyprinodon  learn  to  move  in  a  body  more  read- 

ily than  to  split  into  two  separate  groups  165 

36.  Goldfish  learn  more  readily  if  accompanied  by 

a  trained  leader  166 

37.  An  aquarium-maze  arranged  to  test  the  power 

of  observation  of  fish  168 

38.  Goldfish  react  more  rapidly  if  allowed  to  watch 

others  perform  ^  169 

39.  Flocks  of  hens  are  organized  into  a  definite  so- 

cial hierarchy  178 

40.  Cockerels  also  have  a  social  organization  180 


1 2  ILLUSTRATIONS 

PAGE 

41.  In  flocks  of  pigeons  the  organization  is  one  of 

peck-dominance  rather  than  of  peck-right  187 

42.  The  Dionne  quintuplets  also  show  evidence  of 

a  social  organization  among  themselves  204 

43.  The  percentage  of  births  that  were  canceled  by 

deaths  for  the  given  years  in  Italy  and  Ger- 
many 220 

44.  The  percentage  which  deaths  were  of  births 

steadily  increased  during  the  war  years  223 

45.  Crepidula  fornicata  shows  sex  reversal  254 

46.  Mated  males  of  Crepidula  fornicata  retain  that 

stage  longer  256 

47.  Castes  of  the  common  honey-bee  260 

48.  Some  ant  castes  265 

49.  The  brown  locust  of  South  Africa  has  a  swarm 

phase   which   is    distinct   from    the    solitary 
phase  273 


Foreword 

I  WAS  recently  honored  by  an  invitation  to  give  the 
Norman  Wait  Harris  lectures  at  Northwestern  Uni- 
versity; the  more  so  since  as  one  of  their  side-door 
neighbors  I  live  close  enough  for  my  personal  foibles 
to  be  well  known,  thereby  removing  the  chief  source 
of  any  possible  glamour.  In  this  book  which  grew  out 
of  those  lectures,  as  in  the  lecture  series  itself,  I  make 
no  effort  to  pose  as  the  remote  purveyor  of  a  mys- 
terious erudition;  I  could  not  in  any  case  regard  my- 
self as  more  than  the  exponent  of  the  glorified  com- 
mon sense  which  I  more  and  more  firmly  believe  all 
science  should  be. 

Even  more  than  most,  this  book  is  the  outgrowth 
of  years  of  co-operative  effort.  Some  of  the  basic 
facts  were  collected  with  the  aid  of  funds  from  the 
Rockefeller  Foundation  given  to  aid  biological  re- 
search at  the  University  of  Chicago.  Other  researches 
were  supported  directly  by  that  university  and  more 
recently  by  a  grant  for  the  study  of  the  effect  of 
hormones  on  behavior  from  the  National  Research 
Council. 

13 


x\^ 


1 4  FOREWORD 

In  addition  to  the  personal  aid  received  from  my 
scientific  associates,  many  of  whom  will  be  named  in 
the  text,  the  kindly  criticism  of  Professor  Alfred  E. 
Emerson  has  been  particularly  helpful  in  developing 
the  work  and  in  shaping  the  content  and  implica- 
tions of  these  lectures.  My  thanks  are  given  also  to 
Professor  Sewall  Wright  for  his  criticism  of  Chapter 
IV,  to  Mr.  Kenji  Toda  for  preparing  the  illustra- 
tions and  to  Marjorie  Hill  Allee,  whose  command  of 
the  written  word  has  been  a  constant  resource. 

W.  C.  Allee 
The  University  of  Chicago. 


Mm  Science  versus  Metaphysics 

THE  RATE  of  obsolescence  of  material  things  is 
high.  With  consumers'  goods  we  are  well  aware  of 
this  fact;  and  even  capital  goods  usually  become  out 
of  date  in  a  long  generation.  Last  summer  an  admirer 
of  Will  Rogers  dedicated  a  lasting  monument  to  the 
humorist.  Although  built  for  time  and  erected  in  our 
semi-arid  West  where  decay  is  slow,  the  tower  is  ex- 
pected to  last  only  a  thousand  years.  Invested  capital 
evaporates  even  with  watchful  care;  there  are  few 
private  collections  of  material  wealth  that  remain  in- 
tact a  third  of  a  thousand  years. 

Oddly  enough,  the  most  permanent  contributions 
of  our  age  appear  to  be  the  scientific  discoveries  we 
have  made,  the  artistic  beauties  we  have  created,  and 
the  ideas  we  have  evolved.  To  the  extent  that  these 
advances  are  entombed  in  libraries  and  museums 
they  share  the  impermanence  of  more  material 
things.  A  nearer  approach  to  immortality  is  per- 
mitted those  bits  of  science  and  art  that  escape  from 
the  bindings  of  books  and  pass  into  the  active  life 

IS 


l6  THE  SOCIAL  LIFE  OF  ANIMALS 

and  traditions  of  people.  The  more  widespread  and 
firmly  fixed  these  become  in  the  minds  of  living  men, 
the  greater  is  their  chance  of  longevity. 

The  most  practical  achievement  of  our  extremely 
practical  period  is  the  habit  of  searching  for  new 
truths  and  for  correct  interpretations  of  those  long 
known.  The  unique  contribution  of  the  present  era 
is  not  that  made  by  men  of  business  and  affairs,  spec- 
tacular as  it  may  be.  Rather  this  age  is  and  will 
be  known  as  the  time  of  the  development  and  ap- 
plication of  scientific  methods.  These  contributions 
are  being  made  by  extremely  impractical  research 
workers  who  are  supported  by  a  tiny  splinter  from 
the  great  block  of  capital  gains.  Money  spent  effec- 
tively to  this  end,  whether  in  the  aid  of  research  or 
other  creative  scholarship,  or  in  teaching  the  results 
gained  by  research,  makes  the  most  lasting  and  im- 
portant of  all  modern  investments.  The  most  nearly 
permanent  monument  any  man  can  erect  is  to  have 
influenced  directly  or  indirectly  the  growth  of  im- 
proved ideas  and  traditions  among  the  men  in  the 
street,  in  the  factory  or  on  the  farm. 

It  is  in  this  spirit  that  I  have  undertaken  to  inter- 
pret one  of  the  significant  biological  developments 
of  recent  years.  It  is  my  hope  that  from  the  work 
described  in  these  pages,  all  social  action  may  have  a 
somewhat  broader  and  more  intelligent  foundation. 


SCIENCE  VERSUS   METAPHYSICS  17 

We  can  gain  the  impression  from  some  modern 
oversimplifications  that  science  deals  with  empirical 
facts,  that  philosophy  attends  to  principles  and 
eternal  truths,  and  that  religion  is  concerned  with 
values.  In  the  following  pages  it  will  be  necessary 
to  shake  aside  such  artificial  limits  and  to  present 
principles  along  with  the  evidence  that  supports 
them;  to  test  these  against  experience  and  to  attempt 
frequently  to  weigh  the  general  biological  values 
involved.  This  last  process  will  be  easier  if  we  assay 
survival  values  only.  Admittedly  in  dealing  even 
with  survival  values  we  must  be  relatively  rough 
and  ready  in  our  methods,  and  perhaps  the  conclu- 
sions will  carry  a  strong  odor  of  the  laboratory  in 
which  they  had  their  origin. 

Basically  the  approach  will  be  that  of  the  experi- 
mental biologist  rather  than  that  of  the  theorist, 
which  might  be  more  polished,  or  of  the  philoso- 
pher, which  would  certainly  be  more  abstract  and 
would  probably  use  a  great  many  more  words  for 
the  same  number  of  ideas.  Despite  much  practice 
to  the  contrary,  any  biological  fact  which  concerns 
us  can  be  accurately  described  and  the  conclusions 
from  its  study  be  clearly  expressed  in  relatively  sim- 
ple and  direct  language. 

In  research  reports  and  scholarly  discussions  there 
is  need  for  the  conciseness  and  precision  made  pos- 


l8  THE  SOCIAL   LIFE   OF   ANIMALS 

sible  by  technical  language.  Science  has  no  need, 
however,  and  is  ill-served  by  any  tendency  to  de- 
velop a  cult  of  obscurity.  Scientists  must  be  free  to 
attack  the  unknown  as  effectively  as  they  can  and 
in  return  for  intellectual  freedom  they  have  an 
obligation,  which  rests  heavily  on  those  able  to  do 
so,  to  interpret  research  results  in  terms  which  can 
be  understood  by  intelligent  and  interested  people. 
There  is  current  in  at  least  one  American  uni- 
versity at  present  an  attempt  to  organize  all  knowl- 
edge about  metaphysics,  and  so  secure  a  longed-for 
unity.  In  order  to  obtain  a  simplified  system,  the 
group  of  men  occupied  with  this  enterprise  turn 
back  to  the  days  before  the  present  scientific  era  to 
find  a  statement  of  eternal  principles  which  will 
serve  as  a  unifying  nucleus  for  human  experience 
and  thought.  Such  efforts  at  establishing  a  Neo- 
Scholastic  philosophy,  while  furnishing  an  excellent 
corrective  for  overconfident  scientists,  seem  mis- 
chievously naive  as  a  serious,  present-day  movement. 
We  do  need  relief  from  our  absorbed  attention  to 
conflicting  scientific  detail,  but  progress  must  needs 
come  from  newer  syntheses  which  take  account  of 
the  world  and  man  as  science  sees  them  rather 
than  by  accepting  almost  as  a  whole  some  ancient 
system  of  historical  significance.  These  systems  are  out 
of  date  primarily  because  they  were  evolved  before 


SCIENCE  VERSUS   METAPHYSICS  IQ 

one  of  the  greatest  advances  in  knowledge  that  man 
has  yet  been  able  to  make,  that  of  modern  science. 

Modern  philosophical  educational  systems,  if  they 
are  to  survive,  must  have  as  their  central  core  the 
well-tested  evidence  compiled  by  objective  scientific 
methods.  Such  knowledge  must  have  stood  the  test 
of  being  checked  and  re-checked  by  men  constitu- 
tionally agnostic  in  their  mental  attitudes;  who  can 
say,  "I  don't  know.  What  is  the  evidence?";  who  are 
constantly  seeking  critical  new  evidence  concerning 
the  validity  of  their  ideas. 

An  anecdote  that  is  becoming  classic  among  scien- 
tists will  illustrate  the  point.  Professor  Wood,  phys- 
icist of  Johns  Hopkins,  was  asked  to  respond  to  the 
toast  "Physics  and  Metaphysics"  at  a  dinner  of  some 
philosophical  society.  His  response  was  somewhat  as 
follows: 

The  physicist  gets  an  idea  which  seems  to  him  to 
be  good.  The  more  he  mulls  over  it  the  better  the 
idea  appears.  He  goes  to  the  library  and  reads  on 
the  subject  and  the  more  he  reads  the  more  truth 
he  can  see  in  his  idea.  Finally  he  devises  an  experi- 
mental test  and  goes  to  his  laboratory  to  apply  it. 
As  a  result  of  long  and  careful  experimental  check- 
ing he  discards  the  idea  as  worthless.  "Unfortu- 
nately," Professor  Wood  is  said  to  have  concluded, 
"the  metaphysician  has  no  laboratory." 


History  and  Natural  History 


LIKE  other  human  disciplines,  science  has  its  or- 
thodox and  its  heterodox  views.  The  idea  that  un- 
conscious automatic  co-operation  exists  has  had  a 
long  history,  and  yet  it  is  just  now  beginning  to 
escape  from  the  heterodox  category. 

My  own  interest  in  this  subject  dates  not  from  a 
preconceived  idea  but  from  a  clearly  remembered 
bump  against  some  stubborn  experiments.  Almost 
thirty  years  ago  as  a  graduate  student  in  zoology  I 
was  engaged  in  studying  the  behavior  of  some  com- 
mon small  fresh-water  animals  called  isopods,  tiny 
relatives  of  the  crayfish.  All  fall  and  winter  I  had 
been  collecting  them  from  quiet  mud-bottomed 
ponds,  chopping  the  ice  if  necessary,  and  from  be- 
neath stones  and  under  leaves  in  clear  small  streams. 

I  kept  them  in  the  laboratory  under  conditions 
which  resembled  those  in  which  they  lived  in  na- 
ture. Then  day  after  day  I  put  lots  of  five  or  ten 
isopods  into  shallow  water  in  a  round  pan  that  had 
a  sanded  wax  bottom  so  prepared  that  the  isopods 

20 


HISTORY  AND  NATURAL   HISTORY  21 

could  crawl  about  readily.  When  a  current  was 
stirred  in  the  water  the  isopods  from  the  streams 
usually  headed  against  it;  but  those  from  ponds  were 
more  likely  to  head  down  current,  or  to  be  indif- 
ferent in  their  reaction  to  the  current.  The  behavior 
of  the  two  types  was  sufficiently  different  so  that  at 
first  I  thought  that  stream  and  pond  isopods  repre- 
sented different  species,  but  the  specialist  at  the 
National  Museum  assured  me  that  all  belonged  to 
the  species  appropriately  called  Asellus  communis, 
the  commonest  isopod  of  our  inland  waters. 

Rather  cockily  I  reported  after  a  time  to  my  in- 
structor that  I  had  gained  control  of  the  reaction  of 
these  animals  to  a  water  current.  By  the  judicious 
use  of  oxygen  in  the  water,  I  could  send  the  indif- 
ferent pond  isopods  hauling  themselves  upstream,  or 
I  could  reduce  the  stream  isopods  to  going  with  the 
current.  I  had  not  reckoned  with  another  factor  that 
presently  caught  up  with  me. 

After  a  winter  in  the  laboratory  it  seemed  wise  as 
well  as  pleasant  to  take  my  pan  out  to  a  comfortable 
streamside  one  sunny  April  day,  and  there  check  the 
behavior  of  freshly  collected  isopods  in  water  dipped 
from  the  brook  in  which  they  had  been  living.  To 
my  surprise,  the  stream  isopods,  whose  fellows  all 
winter  had  gone  against  the  current,  now  went 
steadily  downstream  or  cut  across  it  at  any  angle  to 


22  THE  SOCIAL  LIFE  OF  ANIMALS 

reach  another  near-by  isopod.  When  I  used  five  or 
ten  individuals  at  a  time,  as  I  had  done  in  the  labo- 
ratory, they  piled  together  in  small  close  clusters 
that  rolled  over  and  over  in  the  gentle  current. 
Only  by  testing  them  singly  could  I  get  away  from 
this  group  behavior  and  obtain  a  response  to  the 
current;  and  even  this  reaction  was  disconcertingly 
erratic. 

It  took  another  year  of  hard  work  to  get  this  con- 
tradictory behavior  even  approximately  untangled; 
(i)  *  to  find  under  what  conditions  the  attraction  of 
the  group  is  automatically  more  impelling  than  keep- 
ing footing  in  the  stream;  and  that  was  only  the 
beginning  of  the  road  that  I  have  kept  from  that 
April  day  to  this  time,  continuing  to  be  increasingly 
absorbed  in  the  problems  of  group  behavior  and 
other  mass  reactions,  not  only  of  isopods,  but  of  all 
kinds  of  animals. 

As  the  years  have  gone  on,  aided  by  student  and 
other  collaborators  and  by  the  work  of  independent 
investigators,  I  have  tried  to  explore  experimentally 
the  implications  of  group  actions  of  animals.  And 
necessarily,  too,  I  have  had  to  turn  to  the  world's 
literature  to  find  what  others  have  done  and  are 
doing  along  this  line. 

*  Detailed  citations  to  more  complete  statements  will  be  found  in 
the  bibliography. 


HISTORY  AND   NATURAL   HISTORY  23 

A  Greek  philosopher  named  Empedocles  seems 
to  have  had  the  first  recorded  glimmerings  of  an 
idea  of  the  universal  and  fundamental  nature  of 
co-operation  which  underlies  group  action,  as  well 
as  a  conception  of  the  opposing  principle  of  the 
struggle  for  existence.  Empedocles  lived  in  the  fifth 
century  B.C.,  and  he  was  not  only  a  thinker  but  so 
much  a  man  of  affairs  that  he  was  offered  a  king's 
crown,  which  he  refused.  (128) 

He  owes  his  present-day  fame  to  two  long  poems 
in  which  he  outlined  the  idea  that  there  are  natural 
elements:  fire,  earth,  air,  and  water,  which  are  acted 
upon  by  the  combining  power  of  love  and  the  dis- 
rupting power  of  hate.  Under  the  guidance  of  the 
building  force  of  love  the  separate  elements  came 
together  and  formed  the  world.  Separate  parts  of 
plants  and  various  unassorted  pieces  of  animals  arose 
from  the  earth.  These,  Empedocles  taught,  were 
often  combined  and  at  first  the  results  were  mon- 
strous shapes,  which  in  time  became  straightened 
around  until,  still  guided  by  combining  love,  they 
clicked,  to  make  the  more  perfect  animals  we  now 
know.  It  has  taken  us  almost  two  and  a  half  mil- 
lennia to  transmute  this  poetic  conception  into  the 
less  picturesque  but  more  exact  and  workable  ex- 
pression acceptable  to  modern  science. 

After  the  fertile  Greek  era  there  intervened  in  this 


24  THE  SOCIAL   LIFE   OF  ANIMALS 

field  as  elsewhere  the  long  sterile  period  when  Greek 
philosophy,  if  known,  was  dogmatically  accepted, 
and  shared  with  other  authoritarian  systems  the  re- 
sponsibility of  explaining  the  world  of  reality  as  well 
as  the  universe  of  fancy. 

It  was  not  until  my  own  experiments  and  think- 
ing and  reading  had  begun  to  form  in  my  mind  a 
fairly  definite  pattern  that,  by  the  aid  of  Havelock 
Ellis's  The  Dance  of  Life  (43)  I  stumbled  upon  the 
ideas  of  the  third  Earl  of  Shaftesbury,  who  lived  be- 
fore and  after  1700.  He  seems  to  have  been  the  first 
intellectual  in  the  modern  period  to  recognize  fairly 
clearly  that  nature  presents  a  racial  impulse  that  has 
regard  for  others,  as  well  as  a  drive  for  individual 
self-preservation;  that,  in  fact,  there  are  racial  drives 
that  go  beyond  personal  advantage,  and  can  only  be 
explained  by  their  advantage  to  the  group. 

An  unfriendly  contemporary  wrote  pretty  much 
these  words:  "Shaftesbury  seems  to  require  and  ex- 
pect goodness  in  his  species  as  we  do  a  sweet  taste  in 
grapes  and  China  oranges,  of  which,  if  any  are  sour, 
we  boldly  proclaim  that  they  are  not  come  to  their 
accustomed  perfection."  Havelock  Ellis,  in  reviewing 
this  development,  says  that  "therewith  'goodness* 
was  seen  practically  for  the  first  time  in  the  modern 
period  to  be  as  'natural'  as  the  sweetness  of  ripe 
fruit."  It  is  only  fair  to  record  that  in  the  religious 


HISTORY  AND   NATURAL   HISTORY  25 

world  for  at  least  fifty  years  previous  there  had  been 
growing  a  similar  conviction  among  certain  heretics. 

In  1930,  after  having  written  the  text  of  a  care- 
ful account  of  experimental  evidence  concerning  the 
existence  and  non-existence  of  co-operation  at  sub- 
social  levels,  (3)  I  set  down  in  the  draft  of  a  proposed 
preface  that  the  existence  of  such  a  principle  was 
now  for  the  first  time  an  established  fact,  for  which 
the  details  to  follow  gave  full  proof.  I  still  think 
that  the  proof  is  good.  However,  the  preface  as 
published  does  not  contain  any  such  claim,  for  at 
that  point  in  the  writing  I  went  back  and  re-read 
Des  societes  animales  by  the  French  scientist  Es- 
pinas,  (44)  which  appeared  in  1878  and  which  was 
the  pioneering  essay  in  this  field  so  far  as  modern 
work  is  concerned.  There  I  found  Espinas  affirming 
that  no  living  being  is  solitary,  but  that  from  the 
lowest  to  the  highest  each  is  normally  immersed  in 
some  sort  of  social  life,  a  fact  which  he  proclaimed 
sixty  years  ago,  and  added  that  he  was  ready  to  offer 
conclusive  proof. 

I  turned  through  the  pages  past  his  detailed  his- 
tory of  the  evolution  of  ideas  about  the  origin  and 
development  of  society,  and  read  his  massed  evi- 
dence that  communal  life  is  not  "a  restricted  acci- 
dental condition  found  only  among  such  privileged 


26  THE   SOCIAL   LIFE   OF   ANIMALS 

species  as  bees,  ants,  beavers  and  men,  but  is  in  fact 
universal." 

The  evidence  was  largely  based  on  observations 
of  the  existence  of  animal  groupings  in  nature, 
which  are  found  widely  distributed  in  the  different 
levels  of  the  animal  kingdom— facts  such  as  I  shall 
review  later  in  this  chapter.  It  was  clear  to  me  that 
the  facts  which  Espinas  had  found  so  impressive  had 
not  convinced  others  and,  while  suggestive,  did  not 
seem  compelling  to  me  in  the  light  of  other  indica- 
tions to  the  contrary.  Perhaps,  I  cautioned  myself, 
even  the  experimental  evidence  that  I  had  accumu- 
lated in  1930  was  not  really  crucial,  and  it  would 
be  well  to  avoid  making  too  strong  a  claim  in  the 
matter.  The  same  caution  must  continue  even  in  the 
face  of  still  stronger  evidence  known  today. 

The  conclusions  of  Espinas  coming  in  1878  are 
the  more  important  because  the  scientific  world  was 
then,  as  men  in  the  street  are  today,  under  the  spell 
of  the  idea  that  there  is  an  intense  and  frequently 
very  personal  struggle  for  existence  so  important  and 
far  reaching  as  to  leave  no  room  for  so-called  softer 
philosophies.  The  idea  of  the  existence  of  natural 
co-operation  was  apparently  in  the  air  despite  the 
preoccupation  with  this  phase  of  Darwinism.  Kessler 
is  said  to  have  addressed  a  Russian  congress  of  natu- 
ralists on  this  subject  in    1880,  and  from  this  ad- 


HISTORY  AND  NATURAL   HISTORY  2? 

dress  sprang  the  remarkable  if  uncritical  book  by 
the  Russian  anarchist,  Prince  Kropotkin,  on  mutual 
aid.    (74) 

By  combing  the  accumulated  natural  history  rec- 
ords, Kropotkin  was  able  to  collect  observation  after 
observation  which  indicated  that  animals  in  nature 
do  aid  each  other  to  live,  as  well  as,  on  occasion,  kill 
each  other  off.  Kropotkin's  work  served  the  admi- 
rable purpose  of  keeping  this  idea  alive  and  popu- 
larizing it.  It  has  had  also  the  less  fortunate  result 
of  bringing  Kropotkin's  fundamental  doctrine  into 
disrepute  among  students  who  are  critically  sensi- 
tive to  the  value  of  evidence,  and  who  find  that 
Kropotkin's  sources  were  not  always  reliable. 

William  Patten,  an  American  biologist  who  taught 
for  many  years  at  Dartmouth  College,  made  the  next 
general  statement  of  the  fundamental  nature  of  co- 
operation when  in  1920  he  gave  it  a  central  place 
in  his  analysis  of  the  grand  strategy  of  evolution,  (go) 
It  is  of  personal  interest  to  me  that  at  the  scientific 
meetings  in  1919  at  which  I  presented  my  first  ex- 
perimental results  on  this  subject,  Professor  Patten 
gave  a  vice-presidential  address  in  which  he  outlined, 
mainly  from  philosophical  considerations,  his  con- 
clusions concerning  the  importance  of  biological 
co-operation.  He  was  rightly  impressed  by  the  fact 
that  cells  originally  were  separate,  as  protozoans  are 


28  THE  SOCIAL   LIFE   OF  ANIMALS 

today.  Some,  however,  evolved  the  habit  of  remain- 
ing attached  together  after  division.  This  made  a 
beginning  from  which  the  many-celled  higher  ani- 
mals could  develop.  With  each  increase  in  the  ability 
of  cells  to  co-operate  together  there  came  power  to 
increase  the  complexity  of  organization  of  the  cell 
masses.  The  highly  evolved  bodies  of  men  and  of 
insects  are  thus  an  expression  of  increasing  inter- 
cellular co-operation  which  finally  reaches  a  point 
at  which,  for  many  purposes,  the  individual  person 
becomes  the  unit  rather  than  the  co-operating  cells 
of  which  he  is  composed. 

About  the  same  time  the  German,  Deegener,  (40) 
published  an  extensive  treatise  on  the  social  life  of 
animals,  along  the  same  lines  as  the  book  written 
by  Espinas  forty  years  before.  Deegener 's  distinctive 
contribution  was  a  classification  of  the  different 
social  levels,  from  the  simplest  sorts  of  artificial  col- 
lections of  animals  to  parasitism  and  truly  social 
life.  His  rating  of  these  different  aspects  of  sub-social 
and  social  life  in  one  long  outline  has  the  great 
merit  of  showing  that  there  are  no  hard  and  fast 
lines  which  can  be  drawn  between  social  and  sub- 
social  organisms,  but  that  social  communities  are 
the  natural  outgrowth  of  sub-social  groupings.  Un- 
fortunately, wdth  Teutonic  vigor  and  vocabulary, 
he  designated  the  different  categories  in  words  as 


HISTORY  AND   NATURAL   HISTORY  29 

unwieldy  as  they  were  exact.  Bogged  down  by  the 
weight  of  such  terms  as  sympatrogynopaedium,  syn- 
aporium  and  heterosymphagopaedium,  Deegener's 
real  contribution  tends  to  be  lost  even  to  biological 
scholars. 

A  survey  such  as  I  am  attempting  here  should  not 
try  to  be  exhaustive;  I  shall  dismiss  with  a  word  the 
slight  advance  made  by  Alverdes  (16)  and  the  work 
of  many  others  without  that.  There  is,  however, 
another  phase  of  the  literature  whose  reading  has 
given  me  so  much  pleasure  as  well  as  useful  infor- 
mation that  I  shall  not  pass  it  over:  this  deals  with 
the  social  insects.  Espinas,  Kropotkin,  Deegener  and 
Alverdes  of  those  mentioned,  and  a  host  of  others, 
have  written  in  detail  and  in  general  about  these 
fascinating  insects,  but  none  more  accurately  or 
with  greater  insight  and  literary  as  well  as  scientific 
skill  than  the  American  entomologist,  William 
Morton  Wheeler.  His  book  on  Social  Life  Among 
the  Insects,  which  appeared  in  1923,  is  a  noteworthy 
general  summary.  (120)  In  this  he  shows  that  among 
insects  alone,  and  including  such  well-known  forms 
as  termites,  bees,  wasps  and  ants,  and  the  less  gen- 
erally known  social  beetles,  the  social  habit  has 
arisen  some  twenty-four  distinct  times  in  about  one- 
fifth  of  the  known  major  divisions  of  insects.  It 
would  seem  that  there  is  a  general  reservoir  of  pre- 


30  THE   SOCIAL   LIFE   OF  ANIMALS 

social  traits  from  which,  given  the  proper  opportu- 
nity, society  readily  emerges.  Wheeler,  no  less  than 
Espinas,  from  whom  he  quotes,  emphasizes  that  even 
so-called  solitary  species  of  animals  are  of  necessity 
more  or  less  co-operative  members  of  associations  of 
animals  and  that  animals  not  only  compete  among 
themselves  but  they  also  co-operate  with  each  other 
to  secure  mates  and  insure  greater  safety. 

It  did  not,  however,  make  for  the  full  acceptance 
of  these  ideas  that  Wheeler  drew  his  illustrative 
material  primarily  from,  and  based  his  conclusions 
mainly  on,  his  knowledge  of  social  life  among  in- 
sects. The  existence  of  co-operation  among  nest 
mates  in  ants  and  bees  does  not  prove  that  there  are 
beginnings  of  co-operative  processes  among  amoebae 
and  other  greatly  generalized  animals. 

Man  and  the  few  species  of  highly  social  insects 
are  a  small  part  of  the  animal  kingdom;  in  order 
to  discover  and  distinguish  the  principles  of  general 
sociology  it  is  necessary  to  look  farther,  to  focus 
attention  on  the  social  and  anti-social  relationships 
of  many  animals  usually  regarded  as  lacking  social 
life. 

With  and  without  this  end  in  view  there  have 
been  in  the  last  twenty  years  simultaneous  but  inde- 
pendent outbreaks  of  experimentation  on  group 
effects   among  the   lower  animals.   For  a   time  just 


HISTORY  AND   NATURAL   HISTORY  31 

preceding  and  following  1920  we,  who  in  Aus- 
tralia, (107)  in  France  (26)  and  in  the  United 
States  (2)  were  engaged  in  these  studies,  continued 
unaware  of  each  other's  work.  Relatively  soon,  how- 
ever, since  biological  world  literature  is  today  widely 
and  promptly  circulated,  all  such  work,  even  that 
in  Russia,  (53)  became  generally  known.  It  is  these 
general  experiments  on  population  growth,  on  mass 
physiology  and  on  animal  aggregations,  that  are  now 
the  important  aspect  of  the  field  of  animal  co- 
operation. 

I  have  briefly  traced  here  the  history  of  the  idea 
of  innate  co-operation.  One  reason  for  the  slowness 
of  accepting  that  idea  is  the  obvious  fact  that  co- 
operation is  not  always  plain  to  the  eye,  and  that 
competition  in  its  most  non-co-operative  form,  in 
which  no  social  values  are  apparent,  can  readily  be 
observed.  With  certain  exceptions  to  be  nientioned 
soon,  it  has  seemed  that,  social  species  aside,  crowd- 
ing, the  simplest  start  toward  social  life  which  is 
easily  apparent  and  a  condition  of  nearly  all  society, 
was  harmful  alike  to  the  individual  and  to  the  race. 
It  has  been  known  from  experimental  evidence 
since  1854  (62)  that  crowded  animals  may  not  grow 
at  all,  or,  at  any  rate,  gi-ow  less  rapidly  than  their 
uncrowded  brothers  and  sisters.  And  under  many 
conditions  crowded  animals  not  only  do  not  grow. 


32  THE  SOCIAL   LIFE  OF  ANIMALS 

they  die  more  readily,  and  frequently  they  repro- 
duce less  rapidly  than  if  living  in  uncrowded  popu- 
lations. 

All  the  older  works  in  natural  history  taught 
fairly  clearly  that  crowded  groups,  to  have  real  sur- 
vival values,  must  be  sufficiently  well  organized  to 
contribute  to  group  safety  by  warning  of  danger  or 
by  defense  in  case  of  attack.  (3)  If,  in  addition,  these 
groups  are  organized  on  a  basis  of  division  of  labor, 
such  as  occurs  in  the  highly  social  colonies  of  ants 
or  termites,  with  specialized  reproductives,  workers 
and  soldiers,  or  according  to  the  patterns  found  in 
human  society,  then  the  survival  values  of  groups 
are  readily  seen. 

Yet  for  some  reason,  under  natural  conditions  and 
with  very  many  sorts  of  animals,  crowding  in  all 
degrees  does  occur  and  apparently  always  has  oc- 
curred. Conceded  that  animals  do  not  always  act  for 
their  own  best  interests,  still  they  must  do  so  to  a 
certain  degree  or  be  exterminated  in  the  long  run. 
The  advantages  of  the  long-established  habit  of  a 
species  may  not  be  obviously  apparent,  but  it  is  not 
safe  to  say  offhand  that  advantages  do  not  exist. 

There  are  the  dense  crowds  of  certain  animals, 
ladybird  beetles  (Plate  la),  for  example,  that  with 
the  approach  of  winter  collect  in  restricted  and  fa- 
vorable places  where  they  hibernate  together.  Ap- 


PLATE  I.  a.  Ladybird  beetles  cellect  in  dense  ag- 
gregations in  the  autumn  and  hibernate.  /;.  During 
their  breeding  season,  male  midges  gather  in  swarms 
and  await  the  coming  of  .the  females.  (Photographs  by 
Welty.) 


HISTORY  AND  NATURAL   HISTORY  33 

parently,  in  the  face  of  winter  cold,  there  is  some 
safety  in  numbers  even  among  cold-blooded  animals 
that  collect  in  hordes  without  any  organization. 

A  second  plain  exception  to  the  general  testimony 
that  crowding  of  non-social  species  is  harmful  are 
the  aggregations  that  form  during  the  breeding  sea- 
son. Like  the  hibernating  groups,  these  are  very 
widely  distributed  through  the  animal  kingdom. 
Breeding  aggregations  of  worms,  crustaceans,  fishes, 
frogs,  snakes,  birds  and  mammals  or  the  midge  in- 
sects shown  in  Plate  lb,  for  example,  have  long  at- 
tracted attention.  Their  numbers  have  been  great 
enough  and  conspicuous  enough  to  stimulate  re- 
peated descriptions  by  naturalists. 

A  third  exception  is  found  during  times  of  migra- 
tion, when  animals  frequently  crowd  together  in 
great  hordes  and  execute  mass  migratory  movements, 
like  those  of  many  birds. 

However,  breeding,  hibernation  and  migration 
aside,  the  older  information  indicated  that  up  until 
the  point  that  social  life  is  developed,  crowding  is 
harmful. 

But  there  are  many  other  instances  of  crowding 
which  do  not  fall  under  any  of  these  classifications; 
and  it  will  be  worth  while  to  consider  here  the  ex- 
tent and  the  natural  history  of  some  of  these  dense 
animal  aggregations.  Here,  as  elsewhere,  there  will 


34  THE  SOCIAL   LIFE   OF  ANIMALS 

be  no  attempt  to  catalogue  all  known  instances  or 
to  select  merely  the  very  best  cases  known.  I  shall 
try  to  use  examples  that  are  not  too  shopworn  by 
repeated  description. 

Almost  every  observant  person  has  seen  the  soft 
green  "bloom"  which  covers  many  stagnant  ponds. 
Under  the  microscope  this  "bloom"  is  often  seen  to 
be  composed  of  myriads  of  the  tiny  plant-animal 
Euglena.  These  organisms  are  commonly  one-tenth 
of  a  millimeter  long,  which  means  that  in  a  char- 
acteristic layer  of  "bloom"  there  would  be  at  least 
sixty  to  one  hundred  thousand  animals  per  square 
inch;  and  acres  of  water  are  sometimes  covered. 

Lobster-krills  are  small  crustaceans  that  occur  com- 
monly in  shoals  about  the  Falkland  Islands,  Pata- 
gonia, New  Zealand  and  other  southern  waters.  (81) 
A  larval  stage  of  this  animal,  less  than  an  inch  long, 
occurs  often  on  the  surface  of  the  water  in  such 
numbers  that  the  sea  is  red  for  acres;  and  whales  in 
those  waters  simply  open  their  mouths  and  swim 
through  slowly,  feeding  with  no  more  effort  than 
the  process  of  straining  them  out.  These  shrimp- 
like animals  may  be  piled  up  on  the  shore  by  tide 
and  wind  in  stench-producing  layers.  Dampier  wrote 
of  them  in  1700:  "We  saw  great  sholes  of  small  lob- 
sters, which  colored  the  sea  red  in  spots  for  a  mile 
in  compass";  and  they  have  been  known  to  extend 


HISTORY  AND  NATURAL  HISTORY  35 

along  the  Patagonian  coast  for  as  much  as  three  hun- 
dred miles. 

At  Woods  Hole,  on  Cape  Cod,  I  have  at  certain 
seasons  dipped  up  a  bucket  of  sea  water  from  the 
harbor  and  found  more  space  occupied  by  clear, 
jelly-like  ctenophores,  each  the  size  of  a  walnut, 
than  was  taken  by  water.  Sometimes  I  have  dipped 
up  a  fingerbowl  of  sea  water  and  found  it  so  filled 
with  small  pin-point-like  copepods  that  again  there 
seemed  to  be  more  of  them  than  of  the  water  itself. 
These  tiny  relatives  of  the  lobster-krills  are  also  the 
food  of  whales,  and  they,  too,  may  discolor  the 
ocean  for  miles. 

Around  bodies  of  fresh  water,  may-flies  or  midges 
may  emerge  in  clouds.  At  Put-in-Bay,  near  the 
lights  flooding  the  monument  that  commemorates 
Perry's  victory,  I  have  picked  up  living  may-flies  by 
the  double  handfuls  from  the  millions  that  fly  to- 
ward the  lights;  and  near  by  our  lake  boat  steamed 
through  windrows  of  cast  skins  of  the  emerging  may- 
fly nymphs.  Nearer  Chicago  I  have  taken  water 
isopods,  the  half-inch  crustaceans  mentioned  earlier, 
by  the  bucketfuls  from  pools  where  they  had  col- 
lected in  numbers  only  to  be  compared  with  those 
in  twenty  swarms  of  bees. 

We  have  already  spoken  of  the  migratory  hordes. 
Locusts  in  migration  (116)  swarm  out  of  the  sky  in 


36  THE  SOCIAL  LIFE  OF  ANIMALS 

the  Sahara  borderlands,  in  southern  Russia,  in 
South  Africa  and  on  the  Malay  Peninsula  in  ter- 
rorizing numbers  (Figure  1).  They  once  did  so  on  the 
Great  Plains  of  the  United  States,  leaving  a  lively 
memory  of  destruction  that  is  still  roused  by  the 
smaller  migrations  that  may  occur  there  any  summer 

^'''  ^  ■.■:,:■:.    .      ■■  .   -•■•■■■••  \ 


Fig.  1.  A  band  of  grasshopper  nymphs  on  the  march. 
(From  Uvarov,  by  permission  of  the  Imperial  Bureau  of 
Entomology.) 

in  spite  of  active  control  measures.  I  myself  have 
seen  the  so-called  Mormon  cricket  advancing  from 
the  relatively  barren  mountain  pastures  of  Utah 
into  the  green  fields  in  numbers  which  were  not 
halted  by  the  hawks,  turkeys  and  snakes  attendant 
on  the  swarm  and  feeding  greedily;  or  the  active 
assaults  of  men  and  children  warned  out  to  protect 
the  cultivated  lands.  Migrating  army  worms  and 
chinch  bugs  present  equally  impressive  aggregations. 
The  emergence  of  Mexican  free-tailed  bats  from 
the  Carlsbad  cave  of  an  August  evening  has  been 
described  as  a  black  cloud  pouring  out  in  such  den- 
sity as  to  be  visible  two  miles  away.  (19)  Such  bats 


HISTORY  AND  NATURAL   HISTORY  37 

are  estimated  to  hibernate  in  these  caves  by  the 
milHons;  and  they  may  be  found  through  the  day 
in  sleeping  masses  a  yard  across,  hanging  from  the 
roof  like  a  swarm  of  bees. 

Even  larger  mammals  may  collect  into  great, 
closely  packed  herds.  The  migrating  caribou  on 
the  tundra  are  said  to  pour  south  in  hordes  that 
flow  past  a  given  point  for  hours  or  even  for  days. 
And  of  the  antelope  on  the  plains  of  Mongolia,  (17) 
Roy  Chapman  Andrews  says  that  he  has  seen  thou- 
sands upon  thousands  of  bucks,  does,  and  fawns 
pour  over  the  rim  and  spread  out  on  the  plain. 
Sometimes  a  thousand,  more  or  less,  would  dash 
away  from  the  fierd,  only  to  stop  abruptly  and  feed. 
The  mass  of  antelope  were  in  constant  motion  even 
when  the  animals  were  undisturbed.  They  scattered 
before  his  automobile  only  to  re-form  within  a  few 
hours.  In  that  region  only  the  grassland  antelope 
gathers  in  such  immense  herds;  the  long-tailed 
desert  species  never  does  so,  probably  because  there 
is  not  enough  food  to  support  them  in  their  more 
arid  dwelling  place. 

These  are  merely  a  few  of  the  more  dramatic 
instances  of  the  collection  of  great  masses  of  animals 
in  a  small  space.  They  are  more  spectacular  but 
probably  less  important  than  are  the  innumerable 
smaller  aggregations  of  animals  which  are  frequently 


38  THE  SOCIAL  LIFE   OF  ANIMALS 

encountered.  The  small  dense  crowds  of  whirligig 
beetles  are  a  case  in  point.  These  occur  in  wide- 
spread abundance  on  the  surface  of  our  inland 
waters. 

The  more  common  condition  of  less  intense  crowd- 
ing does  not  mean  that  animals  are  usually  solitary. 
Rather,  the  growing  weight  of  evidence  indicates 
that  animals  are  rarely  solitary;  that  they  are  almost 
necessarily  members  of  loosely  integrated  racial  and 
interracial  communities,  in  part  woven  together  by 
environmental  factors,  and  in  part  by  mutual  attrac- 
tion between  the  individual  members  of  the  different 
communities,  no  one  of  which  can  be  affected  with- 
out changing  all  the  rest,  at  least  to  some  slight 
extent. 

Let  us  take  an  example.  Before  the  coming  of  the 
white  man,  and  even  a  century  ago  or  less,  much  of 
the  Great  Plains  was  occupied  by  what  ecologists 
call  a  grassland-bison  community.  (4)  Grasses  could 
readily  grow  in  the  rich  soil,  even  with  the  usual 
summer  dry  spells  and  the  more  severe  cyclic 
drouths  that  occurred  even  then.  By  keeping  the 
grasses  fairly  closely  cropped  the  bison  herds  pre- 
vented the  invasion  of  herbs  and  shrubs  that  might 
have  withstood  the  severities  of  the  climate  but 
could  not  make  headway  against  continual  grazing 
(Plate  II).  In  this  function  the  bison  were  joined  by 


PLATE    II.   A   giasslancl-bison   community.    (Photo- 
graph from  the  National  Park  Board  of  Canada.) 


HISTORY  AND   NATURAL   HISTORY  39 

a  myriad  of  grasshoppers,  crickets,  meadow  mice 
and  prairie  dogs.  All  these  were  key-industry  ani- 
mals. In  one  way  or  another  they  converted  the  grass 
into  meat  of  different  sorts,  on  which  the  plains 
Indians,  buffalo  wolves,  haw^ks,  owls,  and  prairie 
chickens  fed.  If  the  grass  failed,  then  many  of  the 
key-industry  herb-eaters  and  those  that  in  turn  fed 
on  them  must  either  starve,  migrate  into  another 
community  where  they  would  be  disturbing  factors, 
or  change  their  source  of  food  and  thereby  disturb 
the  balance  in  their  own  community. 

It  must  be  pointed  out  here  that  the  plants  of  this 
community  cannot  be  set  off  as  separate  from  the 
animals.  They  divide  the  available  space  between 
them;  they  constantly  interact  upon  each  other  and 
upon  their  physical  environment;  except  for  pur- 
poses of  formal  study  or  in  limited  fields,  the  biolo- 
gist must  consider  both  as  members  of  a  given 
association. 

In  such  a  community  the  effects  of  the  dominant 
bison  were  felt  in  times  of  stress  by  the  humblest 
and  least  conspicuous  grasshopper.  In  the  spring  of 
the  year  hundreds  of  square  miles  normally  sup- 
ported populations  of  six  to  ten  million  insects  and 
other  invertebrate  animals  for  every  acre  of  land. 
As  with  warmer  weather  the  predatory  animals  re- 
turned to  the  grasslands,  these  insects  were  eaten  off 


40  THE  SOCIAL   LIFE   OF  ANIMALS 

until  perhaps  a  tenth  of  their  number  could  be 
found  later  in  the  season;  with  the  autumn  lushness 
they  increased  again,  only  to  fall  back  to  some  half- 
million  or  so  per  acre  during  the  winter  cold. 

Similar  communities  exist  among  aquatic  forms. 
In  fact  one  of  the  first  demonstrations  of  such  a 
community  was  made  for  the  animals  living  in  and 
on  an  oyster-bank.  (82)  A  beautiful  and  penetrating 
description  of  the  interrelations  that  may  be  found 
in  a  small  lake  was  published  not  long  after  by  the 
late  Professor  Forbes  (48)  of  the  Illinois  Biological 
Survey,  in  which  he  pointed  out  that  minnows  com- 
peted with  bladderwort  plants  for  key-industry  or- 
ganisms; and  showed  that  when  a  black  bass  is 
hooked  and  taken  from  the  water  the  triumphant 
fisherman  is  breaking,  unsensed  by  him,  myriads  of 
meshes  which  have  bound  the  fish  to  all  of  the  dif- 
ferent forms  of  lake  life. 

The  existence  of  these  communities  is  now  gen- 
erally recognized,  and  in  order  that  they  may  exist 
it  seems  that  there  must  be  a  far-reaching,  even  if 
vague  and  wholly  unconscious,  co-operation  among 
all  the  living  creatures  of  the  community.  It  is  to 
such  relationships  that  Wheeler  referred  when  he 
said,  "Even  the  so-called  solitary  species  are  neces- 
sarily more  or  less  co-operative  members  of  groups 
or  associations  of  animals  of  different  species." 


HISTORY  AND  NATURAL   HISTORY  41 

Within  these  communities  aggregations  of  animals 
occur  for  a  variety  of  reasons.  Their  nature  can  best 
be  shown  by  a  series  of  illustrations. 

One  variety  of  aggregations  is  that  of  colonial 
forms,  in  which  many  different  so-called  individuals 
remain  through  life  permanently  attached  together. 
In  the  simplest  cases  all  the  individuals  are  alike. 
Each  possesses  a  mouth  and  food-catching  tentacles, 
and  each  feeds  primarily  for  itself,  although  food 
caught  by  one  individual  may  be  shared  with  others 
near  by.  In  more  complex  forms  some  individuals 
have  the  mouths  suppressed,  and  receive  all  their 
food  from  those  that  do  take  food.  They  have  be- 
come specialized  as  bearers  of  batteries  of  stinging 
cells;  they  strike  actively  when  the  colony  is  touched, 
and  their  stinging  cells  explode  so  effectively  as  to 
give  protection  to  the  colony.  Other  individuals  in 
the  same  colony  bear  medusa-like  heads  which  break 
away  and  swim  off,  producing  eggs  and  sperm,  dis- 
tributing them  as  they  drift.  Here  is  certainly  a  divi- 
sion of  labor  though  these  colonial  animals  are 
never  rated  as  social. 

Various  modifications  of  such  colonial  animals 
are  found  particularly  among  the  colonial  protozoa, 
sponges  and  the  coelenterates;  they  also  occur  higher 
in  the  animal  kingdom,  even  among  the  lower 
chordates,  the  great  phylum  to  which  man  himself 


42  THE  SOCIAL  LIFE  OF  ANIMALS 

belongs.  It  is  interesting  that  animals  whose  struc- 
ture forces  them  to  the  sort  of  compulsory  mutual 
aid  that  automatically  follows  such  structural  con- 
tinuity have  never  progressed  far  either  in  social 
achievement  or  in  the  evolutionary  scale.  When 
higher  animals,  such  as  the  lower  chordates,  show 
this  development  they  are  usually  regarded  as  de- 
generate members  of  their  general  stock.  These 
colonial  animals  are  seldom  dominant  elements  in 
the  major  communities  of  which  they  are  a  part. 
One  comes  to  the  conclusion  that  the  more  nearly 
voluntary  such  co-operation  is,  the  greater  its  ad- 
vantage in  social  life.  It  might  on  the  other  hand 
be  pointed  out  that  when  an  animal  has  achieved 
social  organization  and  division  of  labor  low  in  the 
evolutionary  scale,  the  resulting  colonies  are  so  well 
adapted  to  their  environment  that  there  is  not  suffi- 
cient pressure  to  cause  evolutionary  changes. 

A  second  type  of  aggregation  occurs  when  animals 
are  forced  together  willy-nilly  by  the  action  of  wind 
or  tidal  currents  or  waves  over  which  they  have  no 
control,  and  whose  effects  they  cannot  resist.  Many 
of  the  masses  which  lend  color  to  wide  patches  of 
the  ocean  surface  are  brought  together  by  tempo- 
rary or  permanent  currents.  Often  animals  so  dis- 
tributed are  thrown  down  more  or  less  by  chance 
on  types  of  bottom  on  which  they  can  develop,  and 


HISTORY  AND   NATURAL   HISTORY  43 

there,  if  favorable  niches  are  somewhat  rare,  dense 
aggregations  may  result,  like  New  England  coral  on 
a  suitably  hard  bottom,  or  the  animals  found  on  a 
wharf  piling. 

These  accidental  animal  groupings  may  persist 
only  as  long  as  the  physical  forces  which  brought 
them  together  continue  to  act.  Usually,  however, 
they  last  somewhat  longer,  as  a  result  of  a  slightly 
positive  social  inertia  which  tends  to  keep  animals 
concentrated  in  whatever  place  they  happen  to  be 
found.  If  the  groupings  are  to  have  much  perma- 
nence this  quality  of  social  inertia,  the  tendency  of 
animals  to  continue  repeating  the  same  action  in 
the  same  place,  must  be  reinforced  by  another 
quality:  the  social  force  of  toleration  for  the  pres- 
ence of  others  in  a  limited  space.  The  densely  packed 
communities  of  animals  on  a  wharf  piling  can  per- 
sist only  if  toleration  for  crowding  is  well  developed. 

Other  dense  collections  may  be  brought  about  by 
forced  movements  of  animals  in  response  to  some 
orienting  influence  in  their  environment.  These 
oriented,  compelled  reactions  are  frequently  called 
tropisms.  They  are  shown  by  the  moths  or  June 
beetles  or  may-flies  that  collect  about  lights.  Such 
aggregations  are  a  result  of  the  inherited,  internal 
organization  of  the  animals;  and  the  irresistible  at- 
traction of  the  may-fly  to  the  light  is  joined  with 


44  THE  SOCIAL   LIFE  OF  ANIMALS 

active  toleration  for  the  close  proximity  of  others. 

Similarly  close  aggregations  occur  as  a  result  of 
the  less  spectacular  trial  and  error  reactions,  in 
which  the  animals  wander  here  and  there,  more  or 
less  vaguely  stimulated  by  internal  physiological 
states  or  external  conditions,  and  so  come  to  collect 
in  favorable  locations.  Collections  of  animals  about 
limited  sources  of  food  give  a  good  illustration. 
These,  too,  may  show  only  the  social  qualities  of 
inertia  and  toleration. 

A  decided  advance  is  made  when  animals  react 
positively  to  each  other  and  so  actively  collect  to- 
gether, not  primarily  because  the  location  is  favor- 
able or  through  environmental  compulsion,  but  as 
the  result  of  the  beginnings  of  a  social  appetite.  In 
early  stages  of  such  reactions,  the  movement  together 
may  come  primarily  because  the  collection  of  isopods 
or  earthworms  or  starfishes  are  substitutes  for  miss- 
ing elements  in  the  environment. 

Take,  for  example,  the  snake  or  brittle  starfishes 
of  the  New  England  coast.  These  are  rare  now  along 
Cape  Cod,  but  before  the  wasting  disease  swept  away 
the  eel  grass  they  were  abundant  in  favorable  locali- 
ties, but  were  rarely  found  close  together.  I  have 
spent  hours  peering  down  through  a  glass-bottomed 
bucket  here  and  there  and  round  about  in  one  of 
these  localities,  and  have  not  seen  more  than  one 


PLATE  III.  a.  Brittle  starfish  aggregate  readily 
when  put  into  a  bare  vessel  of  sea  watei .  b  shows  con- 
ditions ten  minutes  after  a  was  taken.  (Photographs  by 
Welty.) 


HISTORY  AND  NATURAL   HISTORY  45 

at  a  time.  And  I  have  spent  more  hours  wielding  a 
sturdy  garden  rake  in  swathe  after  swathe  through 
the  short  eel  grass,  very  rarely  pulling  in  more  than 
one  starfish  at  a  haul. 

Yet  when  a  few  brittle  starfishes  are  placed  in  a 
clean  bucket  of  sea  water  they  clump  together  like 
magic  (Plate  III).  In  bare  laboratory  aquaria  they 
remain  so  clumped  for  weeks;  in  fact  the  aggrega- 
tions become  more  compact  as  time  goes  on  as  the 
animals  bring  back  their  extending  arms  and  tuck 
them  into  the  mass.  If,  however,  the  aquaria  are 
dressed  up  by  the  introduction  of  eel  grass  so  that 
conditions  approach  those  found  in  nature,  the  ag- 
gregations disperse  and  the  starfishes  climb  actively 
about  over  the  blades  of  the  eel  grass,  feeding  on 
organisms  and  debris  found  on  their  surfaces. 

The  idea  that  in  clean  laboratory  dishes  these  star- 
fishes are  substituting  each  other  for  the  missing  eel 
grass  was  obvious  and  easy  to  test.  A  kind  of  artifi- 
cial eel  grass  was  made  of  glass  rods  twisted  in 
various  shapes  so  that  they  offered  a  supporting 
framework  for  climbing  in  much  the  same  way  as 
the  true  eel  grass.  So  long  as  the  rods  remained  the 
starfishes  clambered  about  over  the  meshwork  or 
hung  motionless,  usually  isolated.  If  the  rods  were 
removed  they  again  clustered  together. 

As  I  have  said  elsewhere,  (3)  it  is  a  far  cry  from 


46  THE  SOCIAL   LIFE  OF  ANIMALS 

such  aggregations  to  the  groupings  of  foreigners  in 
a  strange  city  that  result  in  Little  Italy,  or  the 
Mexican  settlement,  or  a  German  quarter;  and  yet 
basically  some  of  the  factors  involved  are  similar. 
Perhaps  there  is  a  closer  connection  between  such 
aggregations  in  the  wide  expanse  of  a  clean  aqua- 
rium and  the  schooling  tendency  found  among 
many  fishes  of  the  open  sea;  perhaps  the  same  phe- 
nomenon accounts  for  the  flocking  tendency  of 
many  birds,  as  well  as  mammals  on  the  equally 
monotonous  grassy  seas  of  temperate  plains. 

A  somewhat  different  expression  of  a  positive 
social  reaction  is  shown  when  animals  that  are 
usually  more  or  less  isolated  come  together  and  pass 
the  night  grouped  as  though  they  were  engaged  in 
a  slumber  party.  This  type  of  behavior  has  been 
repeatedly  described  for  different  insects,  even  for 
the  wasps  that  remain  separate  to  such  an  extent 
that  they  are  called  solitary  wasps.  In  some  forms  of 
solitary  wasps  both  males  and  females  are  found  in 
the  sleeping  group.  With  solitary  bees,  such  as  we 
have  near  Chicago,  the  overnight  aggregations  are 
composed  of  males  only.  A  study  which  was  made 
of  the  sleeping  habits  of  a  Florida  butterfly  species 
indicates  that  these  Heliconii  (69)  come  together 
night  after  night  in  the  same  location,  in  part  at 
least  as  a  result  of  place-memory.  The  assemblages 


HISTORY  AND   NATURAL   HISTORY  47 

lack  sexual  significance.  There  is  some  protection  in 
the  fact  that  if  one  is  disturbed  the  whole  group  may 
be  warned.  The  presence  of  many  butterflies  would 
reinforce  any  species  odor  that  might  attract  others 
of  the  same  species,  or  repel  possible  predators. 

The  crowded  roosts  to  which  certain  birds  return 
not  only  for  one  season  but  sometimes  for  years  are 
widely  known.  Here  again  we  are  concerned  with  a 
positive  social  appetite  which  grows  stronger  with 
the  approach  of  darkness;  the  details  as  to  why  and 
how  it  operates  are  not  known. 

Animals  which  come  together  in  intermittent 
groupings  like  these  overnight  aggregations  are 
showing  a  social  appetite  which  is  none  the  less 
real  because  it  is  effective  only  at  spaced  intervals. 
In  this  it  resembles  other  appetites  such  as  those 
for  food,  water  and  sex  relations.  From  such  occa- 
sional or  cyclic  expressions  of  a  social  appetite  it  is 
a  relatively  short  step  to  whole  modes  of  life  which 
are  dominated  by  a  drive  for  social  relationships. 
As  I  have  already  said,  in  the  insects  alone  this  step 
has  been  taken  some  twenty-four  distinct  times  and 
in  widely  separated  divisions  of  that  immense  group. 

Normally  the  development  of  highly  social  life 
comes  by  way  of  an  extension  of  sexual  and  family 
relations  over  greater  portions  of  the  life  span. 
Here  again  all  degrees  of  increased  length  of  asso- 


48  THE  SOCIAL  LIFE  OF  ANIMALS 

elation  can  be  shown,  from  the  sexual  forms  that 
meet  but  once  and  for  a  brief  moment  to  the  ter- 
mite kings  and  queens  that  live  together  for  years. 
Also  all  stages  exist  in  the  evolution  of  the  associa- 
tion of  parents  with  offspring,  from  the  insects  like 
the  female  walking-stick,  which  deposits  eggs  as  she 
moves  about  and  pays  no  more  attention  to  them, 
to  the  ants  and  bees  whose  worker  offspring  spend 
their  entire  lives  in  the  parental  colony  or  some 
colony  budding  off  from  it. 

While  the  extension  of  family  relations  is  very 
obviously  one  potent  method  by  which  social  life  is 
developed  to  a  high  level,  there  are  other  social 
groupings  which  also  deserve  consideration  in  con- 
nection with  the  problem  as  to  the  method  of  evo- 
lution of  social  life.  Schools  of  fish  arise,  for  exam- 
ple, under  conditions  in  which  there  is  no  associa- 
tion with  either  parent  after  the  eggs  are  laid.  At 
times  the  eggs  may  be  so  scattered  in  the  laying  that 
the  schools  form  from  unrelated  individuals.  Here 
the  schooling  tendency  seems  to  underlie  rather 
than  grow  out  of  family  life.  The  mixed  flocks  (22) 
of  tropical  birds  which  are  composed  of  many  spe- 
cies obviously  did  not  grow  directly  from  family 
gatherings,  and  the  groups  of  stags  of  Scottish  deer, 
probably  the  original  stag  parties,  (38)  appear  to 
give  evidence  of  a  grouping  tendency  independent 


HISTORY  AND  NATURAL   HISTORY  49 

of  intersexual  or  family  relations.  This  subject  will 
be  discussed  in  more  detail  in  the  final  chapter. 

The  conclusion  seems  inescapable  that  the  more 
closely-knit  societies  arose  from  some  sort  of  simple 
aggregation,  frequently,  but  not  necessarily,  solely 
of  the  sexual-familial  pattern.  Such  an  evolution 
could  come  about  most  readily  with  the  existence 
of  an  underlying  pervasive  element  of  unconscious 
co-operation,  or  automatic  tendency  toward  mutual 
aid  among  animals. 

In  the  simpler  aggregations  evidence  for  the  pres- 
ence of  such  co-operation  comes  from  the  demon- 
stration of  survival  values  for  the  group.  These  are 
more  impressive  the  more  constant  they  are  found 
to  be.  If  they  exist  throughout  the  year  they  are 
much  more  important  as  social  forerunners  than  if 
present  only  during  the  mating  season  or  at  times 
of  hibernation. 


Ill 


■  Beginnings  of  Co-operation 


WITH  this  chapter  I  begin  the  presentation  of  the 
evidence  for  the  assertion  that  there  is  a  general  prin- 
ciple of  automatic  co-operation  which  is  one  of  the 
fundamental  biological  principles.  The  simplest  ex- 
pression of  this  is  often  found  in  the  beneficial  ef- 
fects of  numbers  of  animals  present  in  a  population. 
Laboratory  work  of  the  last  two  decades  still  shows 
that  overcrowding  is  harmful,  but  it  has  also  uncov- 
ered a  no  less  real,  though  somewhat  slighter,  set  of 
ill  effects  of  undercrowding. 

To  be  sure,  overcrowding  always  produces  ill  ef- 
fects, and  these  can  always  be  demonstrated  at  some 
population  density.  On  the  other  hand,  the  ill  effects 
of  undercrowding  cannot  always  be  shown,  though 
frequently  they  can.  In  generalized  curves  the  mat- 
ter may  be  summarized  thus:  Under  certain  condi- 
tions (g6)  we  find  the  curve  running  like  the  dia- 
gram in  Figure  2  A,  when  height  above  base  line 
gives  the  rate  of  the  biological  action  being  meas- 
ured, and  distance  to  the  right  shows  a  steadily  in- 

50 


BEGINNINGS   OF   CO-OPERATION  51 

creasing  population.  Under  these  conditions  only 
the  ill  effects  of  overcrowding  are  visible,  and  the 
optimum  population  is  the  lowest  possible.  This  is 
the  modern  expression  of  what  used  to  be  called  the 
struggle  for  existence.  In  the  more  poetic  post-Dar- 
winian days  this  struggle  was  thought  of  as  so  in- 
tense and  so  personal  that  an  improved  fork  in  a 
bristle  or  a  sharper  claw  or  an  oilier  feather  might 
turn  the  balance  toward  the  favored  animal.  Now 
we  find  the  struggle  for  existence  mainly  a  matter 
of  populations,  measured  in  the  long  run  only,  and 
then  by  slight  shifts  in  the  ratio  of  births  to  deaths. 

A  second  type  of  phenomena  is  represented  by  a 
curve  with  a  hump  near  the  middle  (97)  as  shown  in 
Figure  2B. 

Again,  height  above  the  base  line  measures  the 
speed  of  some  essential  biological  process  or  proc- 
esses, such  as  longevity;  distance  to  the  right  gives 
increasing  population  densities.  The  harmful  effects 
of  overcrowding,  indicated  by  the  long  slope  to  the 
right,  are  still  plainly  evident,  but  there  is  also  ap- 
parent a  set  of  ill  effects  associated  with  undercrowd- 
ing  which  are  shown  by  the  downward  slope  to  the 
left.  Many  have  written  pointedly  about  overcrowd- 
ing, and  while  there  is  still  much  to  be  learned  in 
that  field,  it  is  in  the  recently  demonstrated  exist- 
ence of  undercrowding,  its  mechanisms  and  its  im- 


52 


THE  SOCIAL  LIFE  OF  ANIMALS 


plications,  that  freshness  lies.  Without  for  one  min- 
ute forgetting  or  minimizing  the  importance  of  the 
right-hand  limb  of  the  last  curve,  it  is  for  the  more 
romantic  left-hand  slope  that  I  ask  your  attention. 


Fig.  2.  A.  Under  some  conditions  the  rate  of  bio- 
logical action  which  is  being  measured  is  greatest  with 
the  smallest  population,  and  decreases  as  the  numbers 
increase.  B.  Under  other  conditions  there  is  a  distinct 
decrease  in  the  rate  of  the  measured  biological  reaction 
with  undercrowding  (to  the  left)  as  well  as  overcrowding 
(to  the  right). 

Perhaps  the  simplest  and  most  direct  demonstra- 
tion of  certain  harmful  effects  of  undercrowding 
comes  from  an  experiment  which  I  understand  is 
carried  on  spontaneously  among  undergraduate  men 
at  certain  universities  and  colleges  of  which  X,  or 
perhaps  better,  Y,  is  an  example.  A  certain  number 
of  men  gather  together  in  a  limited  space  under  arti- 
ficial light  and  undertake  to  consume  a  more  or  less 
limited  amount  of  stronger  or  weaker  alcohol.   If 


BEGINNINGS  OF  CO-OPERATION  53 

there  are  many  men  present  in  proportion  to  the 
amount  of  alcohol,  relatively  little  or  no  harm  will 
result  from  the  experiment.  If  there  are  very  few 
men  and  much  alcohol  there  may  be  garage  bills  and 
other  important  repairs  to  be  made. 

In  one  way  or  another  similar  tests  have  been  car- 
ried out  in  the  laboratory  with  a  variety  of  poisons, 
and  many  kinds  of  animals.  Again  I  choose  from 
the  mass  of  available  evidence  the  results  of  a  simple 
and  clean-cut  experiment  to  illustrate  the  same  point 
with  non-human  animals. 

Everyone  is  acquainted  with  goldfish;  they  are 
hardy  forms  or  else  they  would  not  be  alive  today 
in  so  many  goldfish  bowls.  Colloidal  silver  in  its 
commercial  form  of  argyrol  is  also  well  known.  Col- 
loidal silver,  that  is,  the  finely  divided  and  dispersed 
suspension  of  metallic  silver,  is  highly  toxic  to  liv- 
ing things,  including  even  the  hardy  goldfish. 

In  the  experiment  in  our  laboratory  (8)  we  ex- 
posed sets  of  ten  goldfish  in  one  liter  of  colloidal 
silver,  and  at  the  same  time  placed  sets  of  ten  simi- 
lar goldfish,  one  each,  in  a  whole  liter  of  the  same 
strength  of  the  same  suspension.  This  was  repeated 
until  we  had  killed  seven  lots  of  ten  goldfish  and 
their  seventy  accompanying  but  isolated  fellows. 
Then  when  the  results  were  thrown  together  we  had 
the  simple  table  on  page  54. 


t^-  I 


54  THE  SOCIAL  LIFE  OF  ANIMALS 

TABLE  I 

Survival  in  minutes  of  goldfish  in  colloidal  silver 

NUMBER        NUMBER    DIFFERENCE  STATISTICAL 
GROUPED      ISOLATED  PROBABILITY 

7X  lo       70x1 
182  min.    507  min.     325  min.      P  <  o.ooi 


Any  biological  experiment  has  a  large  number  of 
so-called  variables,  that  is,  of  factors  that  it  is  diffi- 
cult or  impossible  to  bring  under  such  complete 
control  that  we  can  be  certain  that  the  experiment 
will  be  exactly  repeatable  next  time.  Hence  it  is 
customary  to  make  experiments  if  possible  as  paired 
experiments,  in  which  one  set  of  conditions  (those 
of  the  group  in  this  instance)  will  differ  from  an- 
other lot  (those  of  the  isolated  goldfish)  only  by  the 
one  difference,  in  this  case  of  grouping  and  isolation. 
Such  results  with  these  fish  can  then  be  analyzed 
by  statistical  methods  to  find  the  probability  of  get- 
ting like  results  merely  "by  chance."  These  methods 
are  now  so  simple  that  even  I  can  make  the  calcula- 
tions. They  are  as  accepted  a  technique  as  is  the 
paired  experiment. 

With  the  goldfish  there  is  less  than  one  chance  in 
a  thousand  of  getting  as  great  an  average  difference 
with  the  same  number  of  trials.  Technically  we  say 
that  probability,  or  P,  for  short,  is  less  than  0.0001. 


BEGINNINGS  OF   CO-OPERATION  55 

It  means  the  same.  Students  of  statistics  have  found 
that  when  P  z=  0.05  or  less,  that  is,  when  there  are 
fewer  than  five  chances  in  a  hundred  of  such  a  thing 
happening  as  a  result  of  random  sampling  or 
"chance,"  there  is  likely  to  be  something  significant 
in  such  results,  the  more  so  the  smaller  the  fraction 
which  P  is  said  to  equal. 

We  make  such  tests  of  our  experimental  results 
continually,  to  find  how  we  are  getting  on,  and  I 
shall  give  probabilities  repeatedly.  In  doing  so  it 
must  be  remembered  that  these  test  the  data,  not 
the  theory— and  that  the  data  may  vary  significantly 
for  unknown  reasons,  even  when  we  think  we  are 
in  full  control  of  the  situation;  and  that  because 
there  is  only  one  chance  in  one  hundred,  or  ten 
thousand,  or  a  million  that  a  thing  may  happen  by 
"chance"  does  not  mean  that  it  will  never  happen 
through  what  we  call  an  accident;  merely  that  the 
chances  of  its  happening  so,  our  evidence  being  what 
it  is,  are  on  the  order  of  one  in  one  hundred,  or  ten 
thousand,  or  a  million. 

I  will  digress  even  further  into  the  realm  of  coinci- 
dence. A  Negro  friend  of  mine  spent  a  summer  in 
Europe  and  while  in  Paris  visited  the  art  galleries 
of  the  Louvre.  While  there  he  saw  a  Negro  woman 
busy  looking  at  pictures  and  on  coming  closer  dis- 
covered that  she  was  his  own  aunt.  Neither  had  any 


56  THE  SOCIAL  LIFE  OF  ANIMALS 

idea  that  the  other  was  in  Europe.  With  no  pre- 
arrangement,  what  is  the  probability  that  an  Ameri- 
can Negro  from  Chicago  will  meet  his  aunt  in  the 
Louvre?  Yet  it  did  happen  this  once  without  in  any 
way  shaking  the  probability  principle. 

Perhaps  the  digression  is  not  so  great  as  might  ap- 
pear at  first  glance,  for  we  need  a  slight  common 
understanding  of  the  practical  working  of  statistical 
probability;  all  of  modern  science,  the  more  as  well 
as  the  less  exact,  is  built  on  it. 

To  get  back  to  our  goldfish:  those  in  the  groups 
of  ten  lived  decidedly  longer  than  their  fellows  ex- 
posed singly  to  the  same  amount  of  the  same  poison; 
and  significantly  so.  But  why?  Others  had  made  that 
experiment  w^ith  smaller  animals,  and  had  decided 
that  the  group  gave  off  a  mutually  protective  secre- 
tion which  would  protect  that  particular  species  and 
none  other.  One  reason  that  we  were  working  with 
goldfish  was  because  they  are  large  enough  so  that 
we  could  use  approved  methods  of  chemical  analysis 
in  finding  where  the  silver  went.  The  balance  sheet 
from  such  tests  showed  that  we  could  account  for 
all  the  silver  present.  With  the  suspensions  which 
had  held  ten  fish  the  silver  was  almost  all  precipi- 
tated, while  in  the  beakers  that  had  held  but  one  fish 
almost  all  the  silver  was  still  suspended. 

When  exposed  to  the  toxic  colloidal   silver  the 


BEGINNINGS   OF   CO-OPERATION  57 

grouped  fish  shared  between  them  a  dose  easily  fatal 
for  any  one  of  them;  the  slime  they  secreted  changed 
much  of  the  silver  into  a  less  toxic  form.  In  the  ex- 
periment as  set  up  the  suspension  was  somewhat  too 
strong  for  any  to  survive;  with  a  weaker  suspension 
some  or  all  of  the  grouped  animals  would  have  lived; 
as  it  was,  the  group  gained  for  its  members  a  longer 
life.  In  nature,  they  could  have  had  that  many  more 
minutes  for  rain  to  have  diluted  the  water  or  some 
other  disturbance  to  have  cleared  up  the  poison  and 
given  the  fish  a  chance  for  complete  recovery. 

With  other  poisons,  other  mechanisms  become 
effective  in  supplying  group  protection.  Grouped 
Daphnia,  (50)  the  active  water  fleas  known  to  all 
amateur  fish  culturists,  survive  longer  in  over-alka- 
line solutions  than  daphnids  isolated  into  the  same 
volume.  The  reason  here  is  simple.  The  grouped 
animals  give  off  more  carbon  dioxide,  and  this  neu- 
tralizes the  alkali.  Long  before  the  isolated  individual 
can  accomplish  this,  it  is  dead;  in  the  group  those 
on  the  outside  may  succumb,  though  if  the  num- 
ber present  is  large  enough  even  they  may  be  able 
to  live  until  the  environment  is  brought  under  tem- 
porary control. 

Frequently  the  protective  mechanism  is  much 
more  complex.  With  many  aquatic  animals,  other 
things  being  equal,  isolated  animals  consume  more 


58  THE  SOCIAL  LIFE  OF  ANIMALS 

oxygen  than  if  two  or  more  share  the  same  amount 
of  liquid.  By  one  device  or  another,  grouping  fre- 
quently decreases  the  rate  of  respiration.  Several  of 
these  devices  are  known  to  us.  Professor  Child 
showed  many  years  ago  (31)  that  when  animals  are 
exposed  to  a  strongly  toxic  material,  those  with  the 
higher  rate  of  respiration,  though  otherwise  similar, 
die  first.  This  has  been  applied  to  group  biology  by 
direct  tests,  and  it  has  been  shown  that  the  group, 
by  decreasing  the  rate  of  oxygen  consumption  of  its 
members,  makes  them  more  resistant  to  the  action 
of  relatively  strong  concentrations  of  toxic  materials. 

Perhaps  I  have  said  enough  to  show  that  under 
a  variety  of  conditions  groups  of  animals  may  be 
able  to  live  when  isolated  individuals  would  be 
killed  or  at  least  more  severely  injured  by  unaccus- 
tomed toxic,  chemical  elements,  strange  to  their  nor- 
mal environment. 

Will  the  same  relationship  hold  in  the  presence 
of  changes  in  physical  conditions?  There  is  a  con- 
siderable and  growing  lot  of  evidence  that  massed 
animals,  even  those  that  can  be  called  cold-blooded, 
are  harder  to  kill  by  temperature  changes  than  are 
similar  forms  when  isolated.  (51,  126)  This  interests 
us  because  massing  of  such  animals  at  the  onset  of 
hibernation  was  recognized  as  one  of  the  early  ex- 


BEGINNINGS   OF   CO-OPERATION  59 

ceptions  to  the  rule,  now  outgrown,  that  crowding 
is  always  harmful. 

The  exploration  of  temperature  relations  is  a 
time-honored  field.  I  prefer  to  take  up  a  newer 
though  related  area,  that  of  the  effects  of  ultra-violet 
radiation,  in  which  I  shall  present  some  evidence 
so  recently  collected  that  it  has  never  been  reported 
extensively  before.  A  year  ago  Miss  Janet  Wilder 
and  I  began  exposing  the  common  planarian  worm 
of  this  region  to  ultra-violet  radiation,  to  find 
whether  there  was  any  group  protection  from  the 
well-described  lethal  effect  of  ultra-violet  light  on 
these  worms.  (12) 

In  lots  of  twenty,  worms  of  similar  size  and  the 
same  history  were  placed  together  in  a  petri  dish  and 
exposed  to  the  action  of  the  ultra-violet  light  long 
enough  so  that  they  would  disintegrate  within  the 
next  twelve  hours.  Half  of  them,  that  is,  ten  worms, 
were  then  placed  together  in  five  cubic  centimeters 
of  water  and  each  of  the  other  ten  was  put  into  five 
cubic  centimeters  of  similar  water.  Grouped  and  iso- 
lated worms  were  treated  alike  in  every  way,  except 
that  after  irradiation  together,  half  were  grouped  and 
half  were  isolated. 

For  one  purpose  or  another  we  have  repeated  this 
simple  experiment  a  great  many  times  with  a  variety 
of  waters,   and  with   experimental   conditions   ade- 


6o  THE  SOCIAL  LIFE  OF  ANIMALS 

quately  controlled.  Some  of  the  things  we  have  found 
out  are: 

If  the  worms  are  crowded  under  the  ultra-violet 
lamp  so  that  they  shade  each  other,  the  shaded  ones 


RAOIATEO  RADIATED  RAOIATEO  RADIATED 

enOUPEO  6R0UPEO  GROUPED  GROUPED 

reSTCO  TESTED  TESTED  TESTED 

6R0UPEO  SINGLY  GROUPED  SINGLY 


148* 


247' 


RADIATED  RADIATED 

GROUPED  GROUPED 

TESTED  TESTED 

GROUPED  SINGLY 

267' 


IH  168' 
tI  ItI 
ooooojjj HH^oooooJUJ I 


137* 

140    ^M 
P      I 

aooo4jU 


WELL   WATER 


DISTILLED  WATER 


Fig.  3.  Planarian  worms  which  have  been  exposed  to 
ultra-violet  radiation  disintegrate  more  rapidly  if  isolated 
than  if  grouped. 

are  definitely  protected.  When  such  crowding  is 
eliminated  and  by  constant  watching  and  stirring, 
if  needed,  during  exposure,  the  worms  are  kept  ap- 
proximately equally  spaced,  even  then  the  grouped 
worms  survive  longer  than  if  isolated.  Some  of  the 
relationships  are  shown  in  Figure  3. 

Each  block  represents  the  survival  time  of  several 
series  of  worms.  The  figures  at  the  top  of  the  block 
give  the  average  length  of  survival  in  minutes.  The 
blocks  are  constructed  so  that  the  worms  surviving 


BEGINNINGS   OF  CO-OPERATION  6l 

longer,  which  in  each  case  are  the  grouped  worms, 
are  given  as  lOO  per  cent,  regardless  of  the  time 
taken;  while  the  isolated  worms,  which  had  been 
irradiated  in  the  same  dishes  as  their  accompanying 
groups,  survived  on  an  average  of  78  per  cent  and 
77  per  cent  respectively  in  the  two  tests  with  well 
water,  and  only  61  per  cent  in  the  test  in  dis- 
tilled water.  The  numbers  between  the  blocks  show 
the  number  of  worms  averaged  for  each  block;  that 
is,  the  number  of  pairs  of  worms  for  which  results 
are  summarized.  The  statistical  significance  given 
in  terms  of  'T"  is  very  high  in  each  case. 

The  number  present  during  exposure  is  impor- 
tant, as  well  as  the  number  present  during  the  time 
when  it  is  being  determined  how  long  the  animals 
will  survive.  Such  data  are  summarized  in  Figure  4, 
which  is  built  exactly  on  the  same  principle  as  that 
preceding.  Worms  radiated  when  crowded  (left-hand 
block),  and  then  tested  when  isolated,  survived  517 
minutes,  while  accompanying  worms  which  had  been 
radiated  singly  as  well  as  tested  when  isolated,  lived 
only  24  per  cent  as  long.  Those  radiated  in  a  group 
and  tested  singly  (middle  block)  lived  55  per  cent  as 
long  as  those  which  had  been  radiated  in  a  crowd 
and  then  were  isolated  to  observe  the  effects  of  radi- 
ation. It  will  be  remembered  that  these  crowded 
worms    actually    shaded    each    other    and    so    gave 


62  THE  SOCIAL  LIFE  OF  ANIMALS 

physical  protection  from  the  ill  effects  of  ultra-violet 
light.  Finally  (on  the  extreme  right)  is  diagramed 
the  fact  that  worms  radiated  and  tested  singly  lived 
only  62  per  cent  as  long  as  those  radiated  in  a  group 


RAOIATCO  RAOIArCO  RADIATES  RADIATEO  RADIATED  RADIATED 

CROWDED  SINGLY  CROWDED  CROUPtO  GROUPED  SINGLY 

TESTED  TESTED  TESTED  TESTED  TESTED  TESTED 

Singly  singly  Singly  singly  singly  singly 


517'  517'  107' 


WELL  WATER 


Fig.  4.  Planarian  worms  survive  exposure  to  ultra- 
violet radiation  better  if  much  crowded  while  being 
radiated,  or  even  partially  crowded,  even  though  all  are 
isolated  after  a  few  minutes  of  irradiation. 

of  20  per  20  cubic  centimeters  and  also  tested  singly. 
Again  the  figures  give  the  number  of  pairs  tested 
and  under  "P"  the  statistical  probability,  which 
shows  that  all  these  must  be  taken  seriously  even 
though  there  is  decreasing  significance  as  the  per- 
centage of  difference  of  average  survival  time  de- 
creases. 

In  the  two  cases  just  outlined  mass  protection  has 
been  demonstrated,  first  against  the  presence  of  toxic 


BEGINNINGS   OF   CO-OPERATION  63 

materials,  and  second  against  the  ill  effects  of  expo- 
sure to  lethal  ultra-violet  rays.  To  complete  the  pic- 
ture I  have  now  to  describe  the  results  of  exposing 
animals  to  harmful  conditions  in  which  the  difficulty 
is  caused  by  the  absence  of  elements  normally  pres- 
ent in  their  natural  environment.  The  experiment 
has  been  made  on  aquatic  animals  in  a  number  of 
ways,  for  example,  by  putting  fresh-water  animals 
into  distilled  water;  but  it  is  easier  to  demonstrate 
when  marine  animals  are  placed  in  fresh  water. 

Again  I  select  one  experimental  case  from  several 
available.  Near  Woods  Hole,  on  Cape  Cod,  a  small 
flatworm  Procerodes  (Figure  5)  lives  in  certain  re- 
stricted areas  in  large  numbers.  They  are  most  abun- 
dant along  a  stony  stretch  at  about  the  low  tidemark 
or  a  little  beyond  it.  (5)  There,  if  one  finds  the  proper 
location,  one  may  take  from  ten  to  fifty  flatworms 
from  the  lower  surface  of  a  single  stone.  Usually 
they  are  more  or  less  clumped  together.  They  are 
not  easy  to  see  since  each  is  only  a  few  millimeters 
long  and  all  are  of  a  dull  gray  color.  Once  seen, 
they  are  hard  to  detach,  for  the  posterior  end  has  a 
muscular  sucker,  by  means  of  which  the  animal  can 
cling  pretty  securely  even  to  smooth  stones.  When 
these  worms  are  put  into  fresh  water,  pond  water  for 
example,  they  swell  greatly  and  soon  begin  to  dis- 


integrate. 


64 


THE  SOCIAL  LIFE  OF  ANIMALS 


If  these  flatworms  are  washed  thoroughly  to  re- 
move sea  water  from  their  surfaces,  and  then  placed 
in  fresh  water,  a  certain  proportion  of  the  grouped 


Fig.  5.     The  small  marine  flatworm  Procerodes. 

animals  survive  decidedly  longer  than  isolated  worms. 
The  first  worms  to  die  in  the  group  do  so  almost 
as  soon  as  the  first  isolated  worms.  As  the  dead  worm 
disintegrates  it  changes  the  surrounding  water;  we 
say  it  conditions  it;  and  as  a  result  of  this  condition- 
ing the  remaining  worms  of  the  group  have  a  bet- 
ter chance  of  life. 


BEGINNINGS   OF   CO-OPERATION  65 

For  more  careful  experimentation,  a  sort  of  worm 
soup  was  prepared  by  killing  a  number  of  well- 
washed  worms  and  allowing  them  to  remain  in  the 
water  in  which  they  had  died  and  so  condition  it. 
Freshly  collected  Procerodes  lived  longer  in  such 
conditioned  water  than  their  fellows  which  were 
isolated  into  uncontaminated,  clean  pond  water.  The 
difference  between  the  two  waters  was  only  that 
caused  by  the  fact  that  in  one  the  worms  had  died 
and  disintegrated,  while  the  other  was  clean.  This 
difference  in  survival  persisted  even  when,  to  make 
the  test  more  revealing,  the  total  amount  of  salt  in 
the  two  waters  was  made  identical  by  adding  some 
dilute  sea  water  to  the  clean  pond  water.  Results 
from  these  experiments  are  shown  in  Figure  6.  In 
this  chart,  distance  above  the  base  line  gives  the 
percentage  of  survival,  and  distance  to  the  right 
shows  time  of  exposure.  It  will  be  noted  that  the 
worms  lived  decidedly  longer  in  the  conditioned 
water  than  they  did  in  dilute  sea  water  of  the  same 
strength  of  salts. 

The  mechanism  of  this  superficially  mysterious 
group  protection  is  now  known.  (86)  The  dead  and 
disintegrating  worms,  or  more  slowly,  the  living 
worms,  give  off  calcium  into  the  surrounding  water, 
and  calcium  has  a  protective  action  for  marine  ani- 
mals placed  in  fresh  water  or  for  fresh-water  animals 


66 


THE  SOCIAL   LIFE   OF  ANIMALS 


put  into  distilled  water,  a  protective  action  which  is 
out  of  all  proportion  to  its  effect  in  increasing  the 
osmotic  pressure  of  the  water.  We  can  demonstrate 
that  this  is  in  fact  the  mechanism  of  such   group 


1  Conditioned  water 


Fig.  6.  Procerodes  die  more  rapidly  if  transferred  to 
pure  fresh  water  than  in  dilute  sea  water,  but  live 
longer  if  placed  in  fresh  water  in  which  other  Procerodes 
worms  have  died,  even  though  the  total  amount  of  salt 
is  the  same  as  in  the  dilute  sea  water. 

protection.  For  example,  we  can  analyze  the  water 
which  worms  have  conditioned,  find  the  amount  of 
calcium  that  has  been  added,  and  by  adding  that 
amount  directly  get  the  same  results  that  we  do  from 
the  conditioned  water. 

This  explanation  is  not  yet  complete— no  scientific 
explanation  ever  is— but  we  have  demonstrated  that 
what  was  for  a  time  a  very  mysterious  group  pro- 


BEGINNINGS  OF   CO-OPERATION  67 

tection  is  in  fact  in  this  case  an  expression  of  calcium 
physiology.  The  further  developments  on  the  sub- 
ject await  exact  information  concerning  the  details 
of  the  physiological  effects  of  calcium. 

It  is  probably  of  more  direct  human  interest  to 


■;V*i.;::i: 


%^ 


35 


50 


60 


Fig.  7.  Bacteria  frequently  do  not  grow  if  inoculated 
in  small  numbers;  here  different  numbers  of  Bacillus 
coli  were  inoculated  into  a  medium  containing  gentian 
violet. 


know  that  under  many  conditions  bacteria  will  not 
grow  if  only  a  few  are  inoculated  into  an  animal, 
man  for  example;  while  with  a  larger  inoculation 
they  may  grow  abundantly.  (33)  Gentian  violet  is  a 
poison  for  many  bacteria  and  in  regular  medical  use 
for  that  purpose.  In  one  well-studied  case  (Figure  7) 
bacteria  belonging  to  the  species  Bacillus  coli  failed 
to  grow  on  agar  containing  gentian  violet,  if  singly 
inoculated  on  it;  only  when  thirty  or  more  bacteria 


68  THE   SOCIAL  LIFE   OF  ANIMALS 

were  inoculated  did  steady  and  regular  growth  oc- 
cur. With  the  goldfish  spoken  of  earlier,  the  mass 
protection  was  largely  or  wholly  inoperative  when 
the  group  of  ten  was  exposed  to  ten  times  the  amount 
of  toxic  colloidal  silver  to  which  a  single  fish  was 
exposed.  With  these  bacteria,  however,  such  quanti- 
tative limitations  did  not  hold;  thirty  organisms 
were  found  to  fix  at  least  two  hundred  times  the 
amount  of  poison  normally  neutralized  by  an  iso- 
lated bacterium.  This  difference  between  the  change 
which  thirty  bacteria  can  effect  together  as  compared 
with  what  they  can  accomplish  if  isolated  has  been 
called  an  expression  of  the  communal  activity  of 
bacteria.  There  is  a  fairly  large  and  growing  litera- 
ture on  this  subject  which  indicates  that  when  only 
one  or  a  few  bacteria,  even  if  strongly  pathogenic, 
gain  access  to  the  human  body,  they  are  likely  to 
be  killed  by  various  devices  which  aid  in  resisting 
infection.  It  is  fortunate  for  their  victims  that  bac- 
terial infections  normally  tend  not  to  take  unless 
the  inoculum  is  somewhat  sizable  or  unless  a  smaller 
dose  is  frequently  repeated. 

Mass  protection  is  known  to  occur  among  sper- 
matozoa. Many  animals,  especially  those  that  live  in 
the  ocean,  shed  their  eggs  and  spermatozoa  into  the 
sea  water,  and  fertilization  takes  place  in  that  me- 
dium. Dilute  suspensions  of  such  spermatozoa  lose 


BEGINNINGS   OF   CO-OPERATION  69 

their  ability  to  fertilize  eggs  much  sooner  than  if 
they  are  present  in  greater  concentration.  It  is  rou- 
tine laboratory  practice  in  experimenting  with  such 
animals  as  the  common  sea-urchin,  Arbacia,  to  keep 
sperm  in  a  cool  place,  densely  massed  outside  the 
body,  for  hours.  Small  drops  can  be  withdrawn  as 
needed  for  experimentation,  greatly  diluted  and 
used  almost  immediately  to  fertilize  eggs.  When  such 
dilute  suspensions  have  long  since  lost  their  fer- 
tilizing power  the  sperm  in  the  original  dense  mass 
are  still  potentially  as  active  as  ever. 

So  far  we  have  been  considering  mass  effects,  the 
survival  value  of  which,  if  any,  was  shown  by  in- 
creased length  of  life,  often  under  adverse  circum- 
stances. Under  many  different  conditions  and  for  a 
variety  of  organisms,  the  presence  of  numbers  of 
forms  relatively  near  each  other  confers  protection 
on  a  part  of  those  grouped  together  or  even  on  all 
present. 

It  is  possible  to  go  a  step  farther  and  demonstrate 
a  more  actively  positive  effect  of  numbers  of  or- 
ganisms upon  each  other  when  they  are  collected  to- 
gether. Again  I  select  a  fresh  case  for  close  scrutiny; 
that  of  crowding  upon  the  rate  of  development  in 
sea-urchin  eggs. 

Arbacia,  mentioned  above,  is  the  common  sea- 
urchin  of  coastal  waters  south  of  Cape  Cod  (Fig- 


70  THE  SOCIAL  LIFE  OF  ANIMALS 

ure  8).  It  has  been  much  used  in  studies  of  various 
aspects  of  development,  particularly  by  the  biologists 
who  gather  each  summer  in  the  research  laboratories 
at  Woods  Hole,  Massachusetts.  There  are  several 
reasons  for  its  popularity.  These  urchins  are  abun- 


FiG.   8.     Arbacia,   the  common   sea-urchin   of   southern 
New  England,  shown  from  the  upper  surface. 

dant  in  near-by  waters  and  are  readily  mopped  up  by 
the  tubful.  They  can  be  kept  in  good  condition  for 
some  days  in  the  float  cages,  and  eggs  and  sperm 
are  readily  procured  as  needed.  Also  the  breeding 
season  of  Arbacia  extends  through  July  and  August, 
which  are  favored  months  for  research  at  the  seaside. 
For  years  biologists  at  Woods  Hole  have  studied 
the  embryology  and  physiology  of  developing  sea- 
urchin  eggs.  They  have  built  up  a  painstaking, 
almost  a  ritualistic,  technique  for  handling  glassware, 


BEGINNINGS   OF   CO-OPERATION  7  I 

towels  and  instruments.  The  procedures  require  as 
rigid  cleanliness  as  a  surgical  operation.  Conse- 
quently it  was  not  surprising  when  I  first  took  up 
their  study  a  few  years  ago,  to  have  one  of  my  frank- 
est friends  among  the  long-time  workers  on  the  de- 
velopment of  Arbacia,  voice  what  was  apparently  a 
common  feeling  among  them.  He  asked  pointedly 
if  I  thought  I  could  come  into  that  well-worked  field 
and  without  long  training  find  something  they  had 
overlooked.  Such  frank  skepticism  was  refreshingly 
stimulating  and  added  to  the  normal  zest  of  bio- 
logical prospecting. 

The  shed  eggs  of  Arhacia  are  about  the  size  of 
pin  points  and  are  just  visible  to  the  naked  eye.  The 
spermatozoa  are  tiny  things;  the  individual  sperm 
are  invisible  without  a  microscope  although  readily 
seen  when  massed  in  large  numbers.  When  a  few 
drops  of  dilute  sperm  suspension  are  added  to  well- 
washed  eggs,  one  spermatozoan  unites  with  one  q^^. 

After  some  fifty  minutes  at  usual  temperatures,  the 
egg  divides  into  two  cells.  We  call  this  the  first 
cleavage.  Thirty  or  forty  minutes  later  a  second 
cleavage  takes  place  and  thereafter  cleavages  occur 
rapidly.  Within  a  day,  if  all  goes  well,  such  an  egg 
will  have  developed  into  a  freely  swimming  larva. 
Other  things  being  equal,  (lo)  the  time  after  fer- 
tilization to  first,  second  and  third  cleavage  is  speeded 


72 


THE  SOCIAL   LIFE   OF  ANIMALS 


up  for  the  crowded  eggs.  Typical  results  and  some 
of  the  methods  are  shown  in  Figure  9.  With  appro- 


4- mm.' 


FifSt 

Second 
%  cleai/ed 


f^frst 
Second 
%  cieaued. 


58.25 60.25 

85.83 90.25 

99 /GO 


Fig.  9.  Eggs  of  the  sea-urchin,  Arhacia,  cleave  more 
rapidly  in  dense  populations  than  if  only  a  few  are 
present.  Figures  below  the  diagrams,  unless  otherwise 
indicated,  give  time  in  minutes. 

priate  experimental  precautions,  some  eighteen  hun- 
dred eggs  were  introduced  into  a  tiny  drop  of  sea 
water.  Near  by  on  the  same  slide  forty  similar  eggs 
were  placed  in  a  similar  drop  and  the  two  were 
connected  by  a  narrow  strait  as  shown  in  the  figure. 


BEGINNINGS   OF   CO-OPERATION  73 

A  few  eggs  from  the  larger  mass  spilled  over  into 
this  strait.  The  whole  slide  was  placed  in  a  moist 
chamber  to  avoid  drying,  and  examined  from  time 
to  time.  In  a  trifle  over  fifty-five  minutes  half  the 
eggs  in  the  densest  drop  had  passed  first  cleavage.  A 
half-minute  later,  50  per  cent  of  those  in  the  strait 
were  cleaved,  and  twenty  seconds  later  half  of  the 
more  isolated  ones  had  divided.  The  time  to  50  per 
cent  second  cleavage  ranged  between  eighty-four 
minutes  for  the  crowded  eggs  and  over  eighty-six 
and  a  half  minutes  for  the  isolated  ones. 

This  was  repeated  with  four  thousand  eggs  or 
thereabouts  in  the  denser  population,  almost  six 
hundred  of  which  spilled  through  and  formed  a  flat 
apron  over  the  bottom  of  the  second  drop,  in  which 
there  were  thirteen  other  eggs  scattered  singly  about 
the  relatively  unoccupied  space.  Under  these  condi- 
tions the  time  to  50  per  cent  first  cleavage  was  ap- 
proximately fifty-two,  fifty-eight  and  sixty  minutes 
respectively,  and  the  difference  at  the  middle  of  the 
second  cleavage  was  even  greater. 

In  association  with  Dr.  Gertrude  Evans,  who  is  a 
good,  skeptical  research  worker,  this  experiment  was 
repeated  in  many  different  ways;  and  there  remains 
in  my  mind  no  doubt  but  that  under  a  variety  of 
conditions  the  denser  clusters  of  these  Arhacia  eggs 


74  THE  SOCIAL   LIFE   OF   ANIMALS 

cleave  more  rapidly  than  associated  but  isolated 
fellows. 

Under  the  conditions  tested,  the  stimulating  effect 
of  crowding  could  be  detected  when  sixty-five  or 
more  eggs  were  present  in  the  more  crowded  drop 
and  twenty-four  or  fewer  eggs  made  up  the  accom- 
panying sparse  population. 

Within  twenty-four  hours,  under  favorable  condi- 
tions, one  finds  one's  cultures  full  of  free-swimming 
larvae  with  characteristic  arms  which  are  known  as 
plutei.  When  all  our  available  data  collected  the 
first  day  after  fertilization  are  compared  there  is 
again  no  doubt  but  that  the  more  crowded  cultures 
usually  develop  more  rapidly  than  accompanying  but 
sparser  populations.  However,  it  must  be  recorded 
that  throughout  the  whole  series  there  were  occa- 
sional isolated  eggs  that  developed  as  rapidly  as  the 
best  of  the  accompanying  denser  populations.  Such 
eggs  and  embryos  were  exceptional  in  our  experi- 
ence; the  fact  that  they  exist  indicates  clearly  that 
under  the  conditions  of  our  experiments  crowding, 
while  usually  stimulating,  was  not  absolutely  neces- 
sary for  rapid  cleavage  and  early  growth. 

In  this  connection  it  is  interesting  to  note  that 
others  have  prepared  an  extract  from  sea-urchin  eggs 
and  larvae  which  is  growth-promoting,  (91)  and  one 
which  is  growth-inhibiting.  As  has  also  been  found 


BEGINNINGS   OF   CO-OPERATION  75 

with  goldfish,  the  growth-accelerating  principle  seems 
to  be  associated  with  the  protein  fraction  of  the  ex- 
tract. When  the  whole  extract  is  used,  it  is  said  to 
be  growth-inhibiting  and  to  produce  the  same  re- 
sults as  overcrowding.  The  point  I  have  made  is 
that  with  the  sea-urchin  eggs,  under  the  conditions 
of  our  experiments,  there  is  also  an  ill  effect  of  un- 
dercrowding,  and  that  there  is  an  optimum  popula- 
tion size  for  speedy  development  which  is  neither 
too  crowded  nor  too  scattered. 

Much  similar  work  has  been  done  with  the  ef- 
fects of  numbers  on  the  rate  of  multiplication  with 
various  protozoans.  Again  I  shall  have  to  select  re- 
sults from  the  mass  of  available  evidence.  The  late 
T.  Brailsford  Robertson  (107)  of  Australia  an- 
nounced back  in  1921  that  when  two  protozoans  of 
a  certain  species  were  placed  together,  the  rate  of 
division  was  considerably  more  than  double  that 
which  resulted  with  only  one  present.  It  should  be 
noted  that  during  the  time  of  these  experiments  and 
in  all  these  protozoa  which  we  are  considering  re- 
production was  entirely  asexual,  by  self-division  of 
the  original  animal.  I  subjected  the  data  in  Robert- 
son's original  paper  to  statistical  analysis  and  found 
that  there  were  only  thirteen  chances  in  a  thousand 
of  getting  as  great  a  difference  by  random  sampling. 
Such  results  must  be  taken  seriously  (Figure  10). 


76  THE   SOCIAL   LIFE   OF  ANIMALS 

They  were.  And  the  period  after  1921  was  en- 
livened for  some  of  us  by  denials  from  one  first- 
class  laboratory  after  another  that  there  was  anything 
significant  in  Robertson's  data.  Robertson  himself 

ISOLATED  PAIRED 

24  HOURS  20.5  92.4 

RATIO  1  2.2 


I   44 


Wf 


P  =  0.0128 


Fig.  10.  Robertson  found  that  when  two  protozoans 
were  placed  together  each  yielded  over  twice  as  many  as 
when  the  same  number  of  similar  protozoans  were  iso- 
lated. 

rechecked  and  confirmed  his  results,  though  his  ex- 
planations of  them  tended  to  vary.  For  the  moment 
we  are  not  concerned  with  the  explanations;  but 
what  are  the  facts?  The  first  extensive  corroboration 
from  outside  Robertson's  own  laboratory  came  from 
the  work  of  Dr.  Petersen  at  Chicago.  When  she  cul- 
tured the  common  Paramecium  in  small  volumes  of 
liquid,  she  obtained  the  same  results  as  had  Rob- 
ertson's critics,  but  when  she  used  relatively  larger 
volumes  of  the  same  culture  medium,  a  cubic  cen- 


BEGINNINGS   OF   CO-OPERATION  77 

timeter  more  or  less,  she  got  an  increase  in  division 
rate  with  the  presence  of  a  second  individual,  as 
Robertson  had  found  it  in  the  Australian  form  he 
had  studied. 

Still  the  critics  were  not  convinced.  Accordingly 
Dr.  Johnson,  now  of  Stanford  University,  repeated 
this  whole  study  using  a  different  protozoan,  one  of 
the  Oxytricha.  (68)  When  sister  cells  from  pure-line 
cultures  were  used  there  was  no  difference  at  the 
end  of  the  first  day,  whether  the  Oxytricha  were  in- 
troduced singly  or  in  pairs  into  one  or  two  drops  of 
good  medium.  Later,  the  cultures  started  with  one 
organism  always  were  ahead.  With  larger  volumes, 
two  organisms  showed  a  higher  rate  of  reproduction 
per  original  animal  at  the  end  of  the  first  day  than 
if  started  with  a  single  protozoan. 

Again  for  larger  volumes  Robertson's  results  were 
confirmed,  and  those  of  his  critics  for  smaller  vol- 
umes. But  Johnson  had  only  started.  He  knew  from 
the  work  of  others  that  if  a  protozoan  is  washed 
through  several  baths  of  sterile  water  the  associated 
bacteria  are  rinsed  off.  Then  if  the  washed  protozoan 
is  put  into  a  weak  solution  of  the  proper  salts,  into 
which  has  been  introduced  known  numbers  of  the 
bacteria  on  which  they  normally  feed,  the  problem 
can  be  studied  with  a  controlled  food  supply,  both 
as  to  kind  and  amount. 


78  THE   SOCIAL   LIFE   OF  ANIMALS 

This  he  proceeded  to  do.   He  found  a  common 
bacterium  on  which  his  sterile  Oxytricha  would  grow 


NUMBERS    OBTAINED     IN    24-   HOURS    FROM  THE 

ISOLATION    OF    OXYTRICHA    INTO    CONSTANT  VOLUMES 

WITH    DIFFERENT   CONCENTRATIONS    Of  BACTERIA 


CONCENTRN     4X  2X  X  X/4  X/lO 


I 


I 


3.5  9.0  11.4  5.4  3.0 

Fig.  11.  The  ciliate  protozoan  Oxytricha  reproduces 
more  rapidly  with  a  certain  limited  number  of  bacteria 
present  than  with  either  more  or  fewer.  (From  Johnson.) 

and  reproduce  faster  than  in  the  ordinary  medium. 
He  made  standard  suspensions  of  these  bacteria  in 
sterile  salt  solution,  at  what  we  may  call  an  X  con- 
centration. The  bacteria  could  reproduce  little,  if  at 
all,  in  the  salt  medium,  so  that  he  knew  how  much 


BEGINNINGS  OF  CO-OPERATION  79 

and  what  kind  of  fodder  he  was  feeding  his  washed 
protozoans. 

The  resuhs  of  varying  the  amount  of  food  are 


REPRODUCTION-RATE     FOR    24  HOURS    WHEN    ONE    OR    TWO    OXYTRICMA 
ARE     SEEDED     INTO  TWO  DROPS    OF    P.   FLUORESCENS 

CONCCMTRN  4  X 

seeoiNG      t  2 


8.0         tO.2  tO.6        10.4 

Fig.  12.  In  the  denser  suspensions  of  bacteria  the 
protozoans  divide  more  rapidly  when  cultures  are  inocu- 
lated with  two  protozoans  than  if  started  with  a  single 
individual.  (From  Johnson.) 

shown  in  Figure  ii.  With  X  concentration,  in 
twenty-four  hours  one  animal  produced  about  eleven 
progeny.  With  2X  concentration,  isolated  sister  cells 
produced  nine,  and  with  a  4X  concentration  other 
isolated  sister  cells  produced  but  three  and  a  half. 
The  rate  of  reproduction  also  decreased  when  less 
than  X  bacteria  were  present. 


8o  THE  SOCIAL  LIFE  OF  ANIMALS 

Now  he  was  ready  for  the  grand  Robertson  test, 
except  that  by  this  time  nearly  all  the  factors  were 
controlled.  The  results  are  shown  in  the  following 
figure  (Figure  12).  With  X  concentration  it  made 
no  difference  whether  he  started  his  small  cultures 
with  one  or  with  two  sterile  animals.  With  2X  con- 
centration, the  cultures  started  with  two  individuals 
did  as  well  as  in  X  concentration,  but  those  which 
were  started  with  only  one  individual  lagged  defi- 
nitely, producing  only  80  per  cent  as  many  animals 
in  twenty-four  hours.  With  4X  concentration  even 
the  culture  started  with  two  Oxytricha  was  slowed 
down,  but  not  so  much  as  that  started  with  only 
one.  He  had  shown  that  in  the  presence  of  an  ex- 
cess number  of  bacteria,  cultures  seeded  with  more 
than  one  bacterium-eating  protozoan  thrive  better 
than  if  but  one  is  introduced.  Not  content  with  this 
Johnson  took  another  species  and  tried  it  all  over 
again  with  the  same  results. 

From  all  this  careful  work  we  judge  that  the  facts 
on  this  particular  aspect  of  the  effects  of  numbers 
present  on  the  rate  of  asexual  reproduction  seem 
now  to  be  straight;  but  what  about  their  expla- 
nation? This,  as  it  turns  out,  also  interests  us. 
Robertson  advanced  the  following  hypothesis  to 
explain  the  results  which  he  had  observed.  Dur- 
ing division  each  nucleus  retains  as  much  as  pos- 


BEGINNINGS  OF   CO-OPERATION  8l 

sible  of  an  essential,  growth-producing  substance 
with  which  it  was  provided,  and  adds  to  it  dur- 
ing the  course  of  growth  between  divisions.  At 
each  division,  however,  this  substance  is  necessarily 
shared  with  the  surrounding  medium  in  a  propor- 
tion that  is  determined  by  its  relative  solubility  in 
the  culture  water,  and  by  its  affinity  for  chemical 
substances  within  the  nucleus.  The  mutual  speeding 
of  division  by  neighboring  cells  is  due  to  each  cell's 
losing  less  of  this  necessary  substance  because  of  the 
presence  of  the  other.  The  more  of  this  growth-pro- 
moting substance  there  was  in  the  cell,  Robertson 
thought,  the  faster  would  be  the  division  rate;  so 
that  any  circumstance  which  would  conserve  the 
limited  supply  would  tend  to  speed  up  processes 
leading  to  cell  division. 

Stripped  to  essentials  this  hypothesis  says  that  as 
a  result  of  the  presence  of  a  second  organism  both 
lose  less  of  an  unknown  something  which  is  essen- 
tial for  division  than  would  happen  if  but  one  were 
present.  Returning  to  the  problem  after  the  criti- 
cisms of  half  a  dozen  years,  Robertson  affirmed  that 
all  the  data  and  conclusions  on  the  subject  that  had 
been  issued  from  his  laboratory  remained  valid  save 
that  they  might  apply  to  the  ^  associated  food  or- 
ganisms and  not  to  the  protozoans  themselves. 

Johnson  has  paid  considerable  attention  to  this 


82  THE  SOCIAL  LIFE  OF  ANIMALS 

problem,  and  has  concluded  that  the  results  which 
he  has  observed  can  be  explained  as  due  to  bacterial 
crowding;  that  the  larger  number  of  protozoans  in- 
troduced into  dense  cultures  thrive  best  because  they 
are  able  to  reduce  the  bacteria  to  density  optimal 
to  the  protozoa  faster  than  their  isolated  sister  cells 
can;  and  therefore  they  show  a  higher  rate  of  re- 
production. 

This  does  not  seem  to  be  the  whole  story;  for  from 
points  as  distant  as  Baltimore  (79)  and  Jerusalem, 
(101)  I  have  reports  from  trustworthy  men  that  with 
still  simpler  protozoans  they  are  getting  results  which 
suggest  that  some  modification  of  Robertson's  hy- 
pothesis may  be  correct  after  all.  These  organisms 
stimulate  each  other  to  more  rapid  growth  merely 
by  their  presence  in  the  same  small  space. 

With  fine  courtesy,  Professor  Mast  of  Johns  Hop- 
kins has  placed  a  report  of  his  experiments  in  my 
hands  in  advance  of  publication  and  has  permitted 
me  to  summarize  his  results.  He  finds  that  popula- 
tions of  a  flagellate  protozoan  grow  more  rapidly  in 
a  sterile  medium  of  relatively  simple  salts  when 
larger  numbers  are  introduced  than  if  the  cultures 
are  started  with  only  a  few  organisms. 

I  must  not  put  too  much  stress  on  these  reports, 
pending  the  appearance  of  yet  more  data,  but  I 
should  expect  to  find  here,  as  elsewhere,  that  com- 


BEGINNINGS  OF  CO-OPERATION  83 

plicated  problems  such  as  these  that  deal  with  the 
rate  of  population  growth  are  controlled  by  more 
than  one  mechanism. 

The  suggestions  from  the  simpler  protozoans, 
taken  together  with  other  aspects  of  the  mass  physi- 
ology of  protozoa  which  have  been  only  partially 
reviewed  here,  and  with  the  acceleration  of  devel- 
opment demonstrated  for  sea-urchin  eggs,  encourage 
me  to  renew  a  suggestion  made  some  years  ago,  (3) 
which  has,  so  far  as  I  am  aware,  been  overlooked 
to  date. 

Let  us  go  back  to  consider  the  case  of  external 
fertilization  among  aquatic  animals.  When  sperma- 
tozoa and  eggs  are  shed  into  sea  water  by  sea- 
urchins  or  other  marine  animals,  their  length  of 
life  is  distinctly  limited.  If  a  sperm  fails  to  contact 
an  egg  during  the  fertilizable  period,  death  results 
probably  from  starvation  for  the  spermatozoa,  per- 
haps from  suffocation  for  the  egg.  This  means  that 
the  animals  of  the  two  sexes  must  be  fairly  close 
together  if  there  is  to  be  a  union  of  the  shed  sexual 
products.  The  most  vigorous  sperm  of  the  sea- 
urchin  Arhacia  can  travel  in  still  water  about 
thirty  centimeters,  that  is,  about  one  foot  and  two 
inches.  (55)  Spermatozoa  of  these  animals  diluted 
a  few  thousands  of  times  can  survive  from  three  to 
twelve  hours;  the  majority  succumb  by  seven  hours. 


84  THE  SOCIAL  LIFE  OF  ANIMALS 

If  a  current  catches  it,  such  sperm  can  travel  many 
times  thirty  centimeters,  but  even  in  sea  water  the 
sexes  must  be  relatively  aggregated  if  fertilization 
is  to  be  successful.  In  fresh  water,  the  life  of  shed 
gametes  is  much  shorter.  After  ten  minutes,  eggs  of 
the  pike  lose  the  power  to  be  fertilized,  (102)  and 
the  longevity  of  sperm  of  certain  fresh-water  fishes 
is  said  to  be  less  than  a  minute,  so  that  in  fresh 
water  the  aggregation  is  even  more  essential.  With 
animals  that  require  internal  impregnation  the 
necessity  for  close  co-operation  between  at  least 
two  individuals  is  obvious.  Such  considerations  must 
be  fundamental  for  the  long-recognized  breeding 
aggregations  of  animals,  especially  of  those  that  shed 
eggs  and  sperm  into  surrounding  water. 

Mass  relationships  may  be  even  more  important 
sexually,  and  here  I  come  to  the  new  suggestion: 
perhaps  they  had  a  hand  in  shaping  sex  itself.  Pre- 
sumably sexual  evolution  started,  as  it  does  today  in 
plants,  with  a  time  when  all  gametes  of  any  one  spe- 
cies were  similar.  Under  these  conditions  a  first  step 
toward  the  union  of  two  reproductive  elements 
could  be  supplied  by  the  greater  well-being  fos- 
tered by  the  presence  of  more  than  one  gamete 
within  a  limited  area,  as  even  the  simpler  proto- 
zoans are  stimulated  to  asexual  division  today  by  the 
near-by  presence  of  another  of  the  same  species.  In 


I 


BEGINNINGS   OF   CO-OPERATION  85 

the  survival  value  existing  for  separate  living  cells 
before  actual  sexual  union  took  place  we  can  find  a 
logical  beginning  for  the  action  of  selection,  which 
would  in  turn,  with  present  known  values,  result  in 
the  establishment  of  the  sexual  phenomena  as  they 
appear  today.  These  fields  have  not  been  sufficiently 
explored  to  allow  for  more  than  this  flash  of  imagina- 
tion, which  future  researches  may  verify  or  discard. 

At  this  point  it  would  be  well  to  pause  and  look 
back  over  the  road  we  have  traveled  thus  far.  The 
charts,  (7)  shown  as  Figures  13  A  and  B,  show  that 
most  of  our  evidence  has  come  from  fairly  well  down 
among  the  simpler  forms  of  life.  I  have  called  atten- 
tion to  mass  protection  of  one  sort  or  another  among 
bacteria,  planarian  worms,  goldfish  and  the  simpler 
crustaceans.  Actually  there  are  in  scientific  literature 
good  cases  of  mass  protection  for  almost  all  the  ani- 
mals shown  in  these  charts;  and  where  exact  informa- 
tion is  lacking,  as  for  example  among  the  rotifers, 
this  is  a  result  only  of  lack  of  interest  in  conducting 
experiments  on  this  point  with  these  animals.  I  have 
little  doubt  that  we  could,  overnight,  demonstrate 
mass  protection  from  colloidal  silver  for  rotifers;  but 
we  have  more  interesting  work  to  do. 

I  have  also  shown  active  acceleration  of  fundamen- 
tal biological  processes  as  a  result  of  numbers  present 
for  sea-urchin  eggs  and  larvae,  and  for  various  pro- 


Bi(rdM  M&mmalls 


Amphil^ani^    / 


.JZOA 
oeba) 


Ancesrral  plants 


ANCESTRAL  CCELENTERATES 

ANCESTRAL  PROTOZOA  " 

Ancestral    animal-plants  — "^ 
Primitive  protoplasm 
Fig.  13.     A  recent  suggestion  concerning  the  ancestral 
relations  within  the  animal  kingdom.  The  circles  in  A 


B 


CHORDATES 


1^ 


ANCESTRAt  COELENTERATES 


ANCESTRAL  PR0T02OA 


Ancestral  plants 


Ancestral     animal-plants  — 

Primitive  Protoplasm 

and  B  allow  cross-identification.   (From  Allee  in   The 
World  and  Man.) 


88  THE  SOCIAL   LIFE   OF  ANIMALS 

tozoans.  These  have  been  given  in  some  detail,  which 
has  not  left  time  for  similar  demonstrations  among 
regenerating  cells  of  sponges;  nor  have  I  time  to  tell 
how  hydra  have  been  saved  from  depression  periods 
by  the  use  of  self-conditioned  water.  I  have  men- 
tioned but  not  elaborated  the  fact  that  grouped  ani- 
mals frequently  have  different  rates  of  respiration  as 
compared  with  their  isolated  fellows.  This  has  been 
recorded  widely  in  the  animal  kingdom,  notably 
among  planarians,  certain  lower  crustaceans,  some 
starfish,  fishes  and  lizards,  and  for  some,  at  least,  asso- 
ciated survival  values  have  been  demonstrated.  To 
this  extent,  then,  I  have  given  the  crucial  evidence 
I  promised  earlier  that  a  sort  of  unconscious  co- 
operation or  automatic  mutualism  extends  far  down 
among  the  simpler  plants  and  animals. 

These  charts  should  illustrate  one  other  point.  The 
insects  stand  at  the  apex  of  one  long  line  of  evolu- 
tion; mammals  and  birds  are  at  the  peak  of  another 
line  of  evolution;  the  two  have  been  distinct  for  a 
very  long  time.  This  view  of  evolution  indicates  that 
the  ancestral  tree  of  animals  is  not  like  that  of  a  pine 
tree  with  man  at  the  very  top  and  insects  and  all  the 
other  animals  arranged  as  side  shoots  from  one  main 
stem.  Rather,  there  are  at  least  two  main  branches 
which  start  low,  as  in  a  well-pruned  peach  tree.  Both 
rise  to  approximately  equal  heights,  indicating  cor- 


BEGINNINGS   OF   CO-OPERATION  89 

rectly  that  in  their  way  the  insects  are  as  specialized 
as  the  birds  or  mammals.  Since  both  insects  and 
mammals  have  developed  closely-knit  social  groups, 
this  is  further  evidence  that  there  is  a  widely  dis- 
tributed potentiality  of  social  life.  We  shall  return 
to  this  subject  later. 


IV 


Aggregations  of  Higher  Animals 


A  GREAT  deal  of  skepticism  is  necessary  in  science, 
if  progress  is  to  be  even  relatively  steady  and  sound. 
Not  only  must  the  scientist  be  skeptical  of  advance 
reports  of  new  results  until  he  has  seen  the  support- 
ing evidence,  no  matter  how  stimulating  the  thesis 
and  how  well  it  would  explain  material  already 
gathered;  but  in  fields  which  lie  near  his  own  re- 
searches it  is  necessary  if  possible  to  bring  the  prob- 
lem into  his  own  laboratory  and  there  examine  the 
validity  of  the  evidence  itself.  This  repeating  of  ex- 
periments in  order  to  check  the  first  observer  is  some- 
times also  a  testing  of  scientific  courtesy,  but  every 
real  scientist  must  be  prepared  to  submit  to  it  with 
the  best  grace  possible. 

It  is  demanded  also  that  from  time  to  time  one 
should  be  skeptical  of  views  long  held,  and  of  the 
evidence  on  which  they  were  built  up,  particularly 
of  the  inclusiveness  of  the  conclusions  that  have  been 
drawn.  Without  my  own  fair  share  of  this  skepticism 
I  should  never  have  been  drawn  into  what  I  knew 

90 


AGGREGATIONS   OF   HIGHER  ANIMALS  Ql 

from  the  beginning  would  be  a  long  and  laborious 
series  of  experiments  concerning  the  effects  of  num- 
bers present  upon  growth. 

As  long  ago  as  the  eighteen-fifties  Jabez  Hogg, 
(62)  an  Englishman,  found  by  experimenting  that 
crowding  decreased  the  rate  of  growth  of  snails  and 
produced  stunted  adults.  From  that  day  to  this  there 
has  been  almost  no  break  in  the  reported  evidence 
that  overcrowding  reduces  growth;  the  number  of 
reports  that  crowding  in  any  degree  increases  growth 
are  relatively  few. 

This  phenomenon  has,  however,  been  observed  by 
enough  workers  using  animals  widely  distributed 
through  the  animal  kingdom  to  show  that  the  retard- 
ing effect  of  undercrowding  on  growth  is  real.  Before 
considering  the  implications  of  this  statement  let  me 
review  briefly  some  of  the  evidence.  (3)  Here  as  else- 
where I  shall  make  no  attempt  to  catalogue  all  the 
available  evidence;  the  list  would  be  impressively 
long  but  tedious. 

It  is  relatively  easy  to  show  that  mixed  populations 
of  many  animals  grow  faster  than  if  the  same  number 
of  some  one  species  are  cultured  together.  The  com- 
mon experience  of  aquarium  enthusiasts  that  the 
presence  of  the  snails  in  aquaria  increases  the  rate  of 
growth  and  well-being  of  their  fishes  is  a  case  in 
point.  Their  rule-of-thumb  experience  has  been  fully 


9^  THE   SOCIAL   LIFE   OF   ANIMALS 

verified  by  careful  laboratory  experiments.  A  more 
crucial  test  involves  individuals  of  the  same  species: 
all  snails,  let  us  say,  or  all  goldfish.  Is  there  some 
optimum  size  of  the  population  at  which  individuals 
grow  most  rapidly? 

For  years  I  have  been  studying  different  aspects  of 
this  problem  with  the  aid  of  a  succession  of  com- 
petent, critical  research  assistants  and  associates.  The 
names  of  these  young  scientists  are  interesting  and, 
I  think,  important.  They  include  Drs.  Bowen,  Welty, 
Shaw,  Oesting  and  Evans,  and  Messrs.  Livengood, 
Hoskins,  and  Finkel,  all  of  whom  have  independ- 
ently obtained  the  basic  results  I  am  about  to  de- 
scribe. (13,  14,  76) 

We  have  used  goldfish  for  our  experimental  ani- 
mals, because  these  are  inexpensive,  easy  to  obtain, 
hardy  under  laboratory  conditions,  and  able  to  stand 
daily  handling. 

In  order  to  have  a  consistently  constant  water  we 
make  up  a  synthetic  pond  water  by  dissolving  in  good 
distilled  water  salts  of  high  chemical  purity.  Into 
such  water  goldfish  about  three  inches  long  are 
placed  in  sufficient  number  so  that  they  will  give  a 
conditioning  coefficient  of  about  twenty-five.  Let  me 
explain:  this  coefficient  is  obtained  by  multiplying 
the  number  of  fish  by  their  average  length  in  milli- 
meters and  dividing  by  the  number  of  liters  of  water 


AGGREGATIONS   OF   HIGHER  ANIMALS  93 

in  the  containing  vessel.  Living  in  this  water  the  fish 
condition  it  by  giving  off  organic  matter  and  carbon 
dioxide.  They  are  left  in  the  water  for  twenty-one 
hours  or  so,  while  a  similar  amount  of  the  same  water 
stands  near  by  under  exactly  similar  conditions  ex- 
cept for  the  absence  of  fish. 

At  the  end  of  this  time  the  clean  control  water  is 
siphoned  into  a  number  of  clean  jars,  and  a  small 
measured  goldfish  is  placed  in  each.  At  the  same  time 
the  conditioned  water  is  siphoned,  either  with  or 
without  removing  particles  (that  is,  of  excrement, 
etc.)  that  may  be  present,  into  similarly  clean  jars. 
A  set  of  small  measured  goldfish,  like  those  used  in 
the  control  jars,  are  transferred  into  the  conditioned 
water.  These  small  "assay"  fish  have  been  feeding 
for  about  two  hours  before  being  transferred;  the 
larger  conditioning  fish  are  allowed  to  feed  for  a 
somewhat  longer  time  before  being  washed  carefully 
to  remove  food  residues  and  replaced  in  another  lot 
of  water  to  condition  that. 

Meantime  the  jars,  120  of  them,  are  all  washed 
carefully;  and  after  this  is  done  the  experimenter  has 
nothing  more  to  do  until  the  next  day,  except  to  put 
the  laboratory  in  order,  keep  the  temperamental 
steam  distilling  apparatus  running,  test  the  water 
chemically  in  several  ways,  keep  his  records  in  order, 


94  THE  SOCIAL  LIFE  OF  ANIMALS 

and  otherwise  see  that  nothing  untoward  happens  to 
make  him  or  anyone  else  question  the  results. 

After  some  twenty,  twenty-five  or  thirty  days  of 
such  care,  in  which  Sundays  are  included,  again  each 
fish  is  photographed  to  scale,  as  they  were  also  photo- 
graphed at  the  beginning  of  the  experiment;  the 
photographs  are  measured  and  the  relative  growth 
determined  for  the  fish  that  have  daily  been  placed 
into  perfectly  clean  synthetic  pond  water,  as  com- 
pared with  those  which  daily  have  been  put  into 
conditioned  water,  that  is,  into  the  water  in  which 
other  goldfish  have  lived  for  a  day. 

During  the  course  of  an  analysis  of  this  problem 
we  have  performed  this  simple  basic  experiment 
many  times.  The  first  forty-two  such  tests  involving 
886  fish  gave  on  the  average  about  two  units  more 
growth  for  the  fish  in  the  conditioned,  slightly  con- 
taminated water,  than  for  those  in  clean  water  (Fig- 
ure 14).  These  results  have  a  statistical  probability 
(P)  of  about  one  chance  in  a  hundred  million  of 
being  duplicated  by  random  sampling.  Hence  we 
have  demonstrated  that  under  the  conditions  of  our 
experiments  the  goldfish  grow  better  in  water  in 
which  other  similar  goldfish  have  lived  than  they  do 
when  they  are  daily  transferred  to  perfectly  clean 
water. 

The  problem  that  has  been  occupying  us  for  some 


AGGREGATIONS  OF   HIGHER  ANIMALS 


95 


time  is  why  this  is  so.  What  are  the  factors  involved 

that  make  this  slightly  contaminated  water  a  better 

medium  for  young  goldfish  than  a  clean  medium? 

We  have  said  that  the  conditioning  fish  are  fed 


EfFECT  OF  SELF  CONTAMINATED  WATER  ON  GROWTH  OF  GOLDFISH 


«0.  290  274 


I 


GROWTH        1.8  -0  2 


no.  180  142 


I 


I 


GROWTH       1.65  1.00 


MO.         210  120 


CONCErfTRATEO 


I 


I 


GROWTH       2.28  t.ia 


ma       t6l         114 


II 


GROWTH      1.92 


Ha        220  217 


tl 

GROWTH     2.59  2.20 


Fig.  14.  Goldfish  grow  more  rapidly  if  placed  in  vari- 
ous kinds  of  slightly  contaminated  (conditioned)  water. 
The  numbers  above  the  columns  show  the  number  of 
fish  tested.  The  longer  column  represents  the  growth  in 
conditioned  water. 

for  two  or  more  hours  daily  and  are  then  washed 
off  and  placed  in  a  fresh  batch  of  water.  Although 
the  fish  are  never  fed  in  the  water  they  are  condi- 
tioning, within  a  few  hours  after  their  transfer  into  it 
from  the  feeding  aquarium  the  water  becomes  more 
or  less  cloudy  with  regurgitated  food  particles.  These 
bits  of  food  are  large  enough  so  that  the  growth-assay 


96  THE  SOCIAL  LIFE  OF  ANIMALS 

fishes  can  strain  them  out  of  the  water.  When  such 
particles  are  removed  by  filtering,  the  growth-promot- 
ing power  of  the  conditioned  water  is  greatly  les- 
sened, but  it  is  not  completely  lost.  In  our  experi- 
ments we  found  that  suspended  food  particles  ac- 
counted for  80  per  cent  or  more  of  the  increased 
growth  in  conditioned  water  over  that  given  in  clean 
control  water. 

These  experiments  give  certain  suggestions  con- 
cerning some  other  conditioning  factors  that  may  be 
acting.  For  example,  we  know  that  the  skin  glands  of 
fish  secrete  slime  (Figure  15).  When  we  have  made  a 
chemical  extract  of  this  material  we  have  frequently 
recovered  a  growth-promoting  substance,  apparently 
a  protein,  which  was  effective  in  stimulating  growth 
when  diluted  1  to  400,000,  or  even  1  to  800,000  times. 
At  these  dilutions  it  is  not  probable  that  this  factor 
is  affecting  growth  by  furnishing  food  material. 

There  are,  of  course,  other  possibilities,  many  of 
which  we  have  checked.  The  increase  in  growth  is 
not  due,  for  example,  to  a  change  in  the  total  salt 
content  of  the  water,  for  this  does  not  change  in  our 
experiments;  nor  to  differences  in  acidity  or  oxygen, 
nor,  so  far  as  careful  quantitative  analyses  have  re- 
vealed, to  changes  in  chemical  elements  present.  We 
may  be  dealing  with  some  sort  of  mass  protection, 
such  as  was  discussed  in  the  last  chapter,  in  which 


J 


AGGREGATIONS  OF   HIGHER  ANIMALS  97 

the  conditioning  fishes  remove  some  harmful  sub- 
stance, but  of  this  we  have  no  real  evidence. 

Whatever  the  explanation,  we  are  certain  of  the 
facts,  and  we  know  that  we  have  demonstrated  a  de- 


EFFECT   OF   PROTEIN   EXTRACT   FROM  SKIN   OF 
GOLDFISHES    ON  GROWTH   OF   GOLDFISH 


NO.  56  59 


EXTRACT 

VS.  ■■  P=  0.0106 


CONTROL 


. 


GROWTH       1,95  0.54 


NO.  61  122 


EXTRACT 

VS. 

SALT  CONTROL 


GROWTH        3.22  0.61 


P=  0.0006 


NO.  26  28 


EXTRACT 

VS. 

CONDITIONED 

WATER 


II 


GROWTH       1.92  1.55 


P=  0.26 


Fig.  15.  An  extract  from  the  skin  of  goldfish  fre- 
quently has  growth-promoting  power.  The  arrangement 
of  the  figure  is  on  the  same  plan  as  was  used  in  Fig.  14. 


98  THE  SOCIAL   LIFE   OF  ANIMALS 

vice  such  that  if  in  nature  one  or  a  few  fish  in  a 
group  find  plenty  of  food,  apparently  without  will- 
ing to  do  so  they  regurgitate  some  food  particles 
which  are  taken  by  others,  a  sort  of  automatic  shar- 
ing. Again,  in  water  that  changes  rapidly,  such  stag- 
nant-water fishes  as  goldfish,  if  present  in  numbers, 
are  able  to  condition  their  environment,  perhaps  by 
the  secretion  of  mucus,  so  that  it  becomes  a  more 
favorable  place  in  which  to  live  and  grow. 

Perhaps  I  have  lingered  too  long  over  this  one 
case;  I  am  so  close  to  the  facts  and  to  the  tactics  used 
in  collecting  them  that  they  may  seem  rnore  interest- 
ing to  me  than  they  will  ten  years  hence.  We  have 
run  the  same  experiment  with  positive  results  with 
a  few  other  species  of  fishes;  and  we  have  also  found 
by  experimentation  that  certain  fish  will  regenerate 
tails  that  have  been  cut  off  if  several  are  present  in 
the  same  water  more  rapidly  than  if  each  is  isolated. 
(112)  The  same  is  true  for  the  young  tadpoles  of  sala- 
manders, with  which  we  have  had  experience.  The 
explanation  of  the  more  rapid  regeneration  of  such 
cut  tails  is  probably  relatively  simple.  The  several 
animals  together  more  readily  bring  the  surrounding 
fresh  water  to  approximately  the  salt  content  of  the 
cut  and  regenerating  tissues  than  can  be  done  by  a 
single  animal  placed  in  the  same  amount  of  water. 


AGGREGATIONS   OF   HIGHER  ANIMALS  QQ 

This  may  not  be  the  whole  of  the  story  but  it  is  prob- 
ably a  significant  part  of  it. 

In  both  of  these  cases  the  additional  growth  of 
aquatic  animals,  which  occurs  as  a  result  of  the  pres- 
ence of  other  animals  of  the  same  species,  is  produced 
in  response  to  some  sort  of  chemical  which  has  been 
given  off  into  the  surrounding  water.  This  may  be 
nothing  more  than  the  unswallowing  of  surplus  food 
by  the  conditioning  fish.  With  animals  whose  tails 
have  been  freshly  cut  off  the  addition  of  salts  to  the 
water  by  the  group  may  balance  the  osmotic  tension 
at  the  cut  surfaces  and  so  favor  re-growth.  The  excit- 
ing result  of  these  studies  lies  in  the  suggestion  that 
some  less  obvious  growth-promoting  substances  may 
also  be  secreted  into  the  surrounding  water. 

Animal  aggregations  frequently  produce  physical 
as  well  as  chemical  changes,  and  while  we  are  con- 
sidering the  effect  of  numbers  of  animals  present  on 
the  rate  of  growth  of  individuals  it  is  interesting  to 
examine  one  case  in  which  growth-promotion  appears 
to  have  been  produced  largely  by  changes  in  tempera- 
ture. Such  an  effect  has  been  reported  more  than 
once;  it  is  most  simply  illustrated  in  a  warm-blooded 
animal,  this  time  the  white  mouse.  The  experiment 
was  first  performed  in  Poland,  but  the  causal  factors 
were  then  only  partially  recognized.  It  has  been  re- 


lOO  THE  SOCIAL  LIFE  OF  ANIMALS 

peated  in  our  laboratory  where  significant  steps  have 
been  taken  towards  its  further  analysis. 

Vetulani,  the  original  experimenter,  (117)  used 
closely  inbred  mice  for  his  experimental  animals.  He 
measured  the  growth  of  males  and  females  separately 
from  the  sixth  and  on  through  the  twenty-second 
weeks  of  their  lives.  After  rearrangement  he  followed 
them  for  ten  weeks  longer  as  a  sort  of  control.  Fresh 
food  was  supplied  in  abundance  each  day,  and  proper 
experimental  conditions  seem  to  have  been  main- 
tained. 

Growth  during  the  first  sixteen  weeks  of  the  ex- 
periment is  shown  in  the  accompanying  graphs  (Fig- 
ure 16).  All  started  off  at  approximately  the  same 
rate.  After  the  fifth  week  of  the  experiment,  however, 
it  is  clear  that  the  isolated  mice  were  growing  most 
slowly,  and  they  continued  to  do  so  as  long  as  the 
experiment  ran.  The  most  rapid  rate  of  growth  was 
observed  in  those  mice  which  were  placed  two  to 
four  per  cage;  those  five  to  six  per  cage  grew  next 
best,  and  only  slightly  below  these  came  those  living 
nine  to  twelve  per  cage. 

Under  the  conditions  of  this  experiment  the  iso- 
lated young  mice  were  most  handicapped,  those  most 
crowded  were  next,  while  those  that  were  somewhat 
but  not  too  crowded  grew  most  rapidly.  When  the 
mice  were  rearranged  for  a  continuing  period  of  ten 


OK — I 1 1 1 1 1 1 1 1 t       I       I       I       I       .       I 

6      7      8      9     10    11121314    15    1G17    1819   20   2I22 
A;,'c  in  weeks 

Fig.  i6.  White  mice  grow  faster  in  small  groups  than 
in  large  ones;  they  grow  slowest .  when  isolated  (solid 
line).  (From  Vetulani.) 


102  THE  SOCIAL  LIFE  OF  ANIMALS 

weeks  the  same  relations  held,  showing  that  it  was 
the  state  of  aggregation  rather  than  individual  dif- 
ferences between  mouse  and  mouse  which  was  impor- 
tant in  producing  the  differences  in  growth  rates. 

Mr.  Retzlaff,  (105)  the  student  who  brought  this 
work  into  our  laboratory,  tried  first  to  repeat  Vetu- 
lani's  experiments  in  a  room  held  at  relatively  high 
temperatures  (29-30°  C).  Under  these  conditions  he 
found  that  insofar  as  significant  differences  existed 
they  showed  that  most  rapid  growth  occurred  with 
the  isolated  mice.  When,  however,  he  lowered  the 
room  temperature  to  about  16°  C.  he  obtained  the 
same  general  effect  as  reported  by  Vetulani.  It  would 
seem  then  that  in  this  case  the  opportunity  to  keep 
warm  in  a  chilling  temperature  is  one  of  the  main 
factors  in  promoting  growth  of  the  crowded,  but  not 
too  crowded,  animals.  This  conclusion  is  strength- 
ened by  recent  analyses  of  the  temperature  relations 
of  mice,  made  by  French  physiologists,  (30)  which 
show  that  a  mammal  as  small  as  a  mouse  has  great 
difficulty  in  maintaining  a  constant  temperature  and 
rarely  does  so  for  extended  periods  of  time.  A  change 
of  external  temperature  from  30°  to  18°  C.  will  cause 
a  lowering  of  0.4°  in  the  body  temperature  of  a 
resting  mouse. 

With  such  temperature  lability  it  is  easy  to  see  that 
a  few  mice  huddled  together  as  is  their  habit  could 


AGGREGATIONS   OF   HIGHER  ANIMALS  IO3 

help  each  other  maintain  their  internal  temperatures, 
conserving  energy  for  growth,  while  if  isolated  they 
must  use  much  of  their  energy  in  keeping  warm. 

Vetulani  observed  another  factor  at  work.  Some 
of  his  mice  had  lesions  of  the  skin  which  they  treated 
by  licking.  When  these  were  in  the  head  region  they 
could  only  be  treated  by  another  individual.  Some 
of  his  isolated  mice  had  such  lesions  when  at  the  end 
of  the  first  experimental  period  they  were  re-grouped 
for  further  observation;  these  wounds  were  soon 
cured  by  their  new  nest  mates. 

When  one  turns  from  studying  the  rate  of  growth 
of  individuals  to  that  of  populations  of  these  higher 
sexual  animals,  many  of  the  same  principles  can  be 
observed  working  as  were  outlined  in  the  last  chap- 
ter for  the  growth  of  asexual  populations  of  proto- 
zoans in  which  overcrowding  retards  population 
growth,  while  optimal  crowding,  at  least  in  many 
instances,  favors  it. 

With  experimental  populations  of  mice,  for  exam- 
ple, three  long,  laborious  experiments  made  in  Scot- 
land (36)  and  in  Chicago  (106)  have  indicated  that, 
under  the  conditions  tried,  the  least  crowded  mice 
reproduce  most  rapidly.  The  same  holds  true  for  the 
well-studied  fruit-fly,  Drosophila.  (96) 

Neither  with  these  flies  nor  with  the  mice  is  there 
any  indication  to  date  of  a  more  rapid  rate  of  repro- 


104  THE  SOCIAL   LIFE   OF  ANIMALS 

duction  per  female  when  more  than  the  minimal 
pair  is  present.  I  have  a  strong  suspicion,  however, 
that  one  would  get  a  more  rapid  rate  of  increase  per 
number  of  animals  involved  if,  instead  of  keeping 
the  sexes  equal  in  numbers,  there  were  a  ratio,  let 
us  say,  of  two  females  to  one  male. 

We  do  know  that  with  Drosophila  the  greatest 
numbers  are  produced  when  the  feeding  surface  is 
relatively  great  but  not  too  great;  (60)  this  result  may 
be  explained  by  the  assumption  that  with  too  great 
space,  or  in  other  words,  with  too  few  flies  present, 
wild  yeasts  or  molds  grow  more  rapidly  than  the 
Drosophila  can  keep  under  control. 

Another  well-studied  laboratory  animal,  the  flour 
beetle,  Triholium,  under  certain  experimental  con- 
ditions gives  most  rapid  population  growth  at  an 
intermediate  population  size  rather  than  with  too 
few  or  too  many  present.  A  study  of  data  collected 
by  Chapman  showed  that  in  a  flour  beetle's  little 
world,  a  microcosm  of  thirty-two  grams  of  flour,  these 
beetles,  during  the  early  stages  of  population  growth, 
reproduce  most  rapidly  per  female  with  two  pairs 
present  (Figure  17).  Reproduction  is  more  rapid 
when  four  pairs  or  even  sixteen  pairs  are  present, 
than  if  there  is  only  one  pair.  (3) 

This  work  of  Dr.  Chapman's  was  done  for  another 
purpose.  We  took  it  for  an  indication  of  possibilities. 


AGGREGATIONS  OF   HIGHER  ANIMALS  IO5 

and  Dr.  Thomas  Park  looked  into  the  matter  inde- 
pendently. (88)  He  found  the  situation  very  much 
as  it  had  originally  appeared  to  be.  A  Scotsman 
named  Maclagen  had  a  curiosity  along  the  same  line 


8 

. 

S^'^ 

/' 

^N< 

"§ 

/' 

"^^^^^^ 

^6 

Ji 

\*^^>^^ 

\      ^^^^^^^^^ 

/' 

\^       ^""X^ 

554 

/ 

\                        ^^frdays 

^  5 

P 

v.. 

i? 

/' 

*"'••. ^ 

2 

// 

""-..SSc/ays 

1 

1 « I 1 1 

2  4  8  16  32  64 

/nitiaC  population  per  ^2  Sms,  of  f/oar 

Fig.  17.     Flour  beetles  reproduce  more  rapidly  if  more 
than  one  pair  is  present. 

and  independently  re-checked  the  whole  matter  with 
the  same  results.  (77)  Three  separate  workers  in 
three  different  laboratories  have  now  obtained  essen- 
tially similar  results  with  these  same  beetles,  and  the 
chances  that  all  are  mistaken  are  rather  remote. 

One  of  them,  Dr.  Thomas  Park,  has  proceeded  to 
analyze  the  factors  involved.  (89)  He  finds  that  the 
results  come  from  the  interaction  of  two  opposing 
tendencies.  In  the  first  place,  adult  beetles  roam  at 


106  THE   SOCIAL   LIFE   OF  ANIMALS 

random  through  their  floury  universe.  They  eat  the 
flour,  but  they  may  also  eat  their  own  eggs  as  they 
encounter  these  on  their  travels.  This  habit  of  egg- 
eating  tends  to  reduce  the  rate  of  population  growth, 
the  more  so  the  denser  the  population. 

The  second  factor  is  the  experimentally  proven 
fact  that  up  to  a  certain  point  copulation  and  suc- 
cessive re-copulation  stimulate  the  female  Tribolium 
beetles  to  lay  more  eggs,  and  eggs  with  a  higher  per- 
centage of  fertility.  Thus  the  more  dense  the  beetle 
population  the  more  rapid  its  rate  of  increase.  The 
interaction  of  these  two  opposing  tendencies  results 
in  an  intermediate  optimal  population  in  which 
more  offspring  are  produced  per  adult  animal  than 
in  either  more  or  less  dense  populations. 

It  may  be  felt  that  I  have  been  keeping  too  closely 
to  the  more  or  less  artificial  conditions  found  in  the 
laboratory.  It  is  true  that  in  an  attempt  to  bring  the 
various  aspects  of  the  population  problem  under  ex- 
perimental control  we  have  avoided  those  field  obser- 
vations which  can  only  be  recorded  as  more  or  less 
interesting  anecdotes.  We  have  now  come  to  a  point 
in  our  inquiry,  however,  at  which  it  is  necessary  to 
move  directly  into  the  field. 

Given  the  evidence  at  hand,  that  optimal  numbers 
present  in  a  given  situation  have  certain  positive 
survival  values  and  some  definitely  stimulating  effects 


AGGREGATIONS  OF   HIGHER  ANIMALS  107 

on  the  growth  of  individuals  and  the  increase  of 
populations,  we  strike  the  problem  of  the  optimal 
size  of  a  population  in  nature.  This  is  an  exceedingly 
difficult  question  on  which  to  obtain  data.  Suppose, 
therefore,  that  we  simplify  it  by  asking  what  minimal 
numbers  are  necessary  if  a  species  is  to  maintain  itself 
in  nature? 

This  inquiry  is  a  direct  attempt  to  find  under  nat- 
ural conditions  the  application  of  the  statement  by 
Professor  Pearl  that  "this  whole  matter  of  influence 
of  density  of  population  in  all  senses,  upon  biological 
phenomena,  deserves  a  great  deal  more  attention 
than  it  has  had.  The  indications  all  are  that  it  is  the 
most  important  and  significant  element  in  the  bio- 
logical, as  distinguished  from  the  physical,  environ- 
ment of  organisms." 

Over  and  over  again  in  the  last  half-dozen  years 
I  have  asked  field  naturalists,  students  of  birds,  wild- 
life managers,  anyone  and  everyone  who  might  have 
had  experience  in  that  direction,  how  few  members 
of  a  given  species  could  maintain  themselves  in  a 
given  situation.  Always  until  this  last  summer  I  have 
found  that,  stripped  of  extra  verbiage  behind  which 
they  might  hide  their  ignorance,  the  real  answer  was 
that  they  did  not  know. 

And  then  I  had  two  pieces  of  luck;  I  found  a  man 
and  a  scientific  paper.  My  friend.  Professor  Phillips 


lo8  THE  SOCIAL  LIFE   OF  ANIMALS 

of  South  Africa,  came  to  spend  some  weeks  with  us. 
He  told  us  that  the  Knysna  Forest,  a  protected  wood- 
land in  South  Africa,  has  an  area  of  225  square  miles, 
fifteen  miles  on  a  side,  and  that  this  forest  is  the 
home  of  a  herd  of  eleven  elephants,  which  can  also 
range  outside  the  forest  limits.  On  the  other  hand, 
the  Addo  Forest,  of  twenty-five  to  thirty  square  miles, 
supports  a  herd  of  twenty-four  elephants.  (98)  Dr. 
Phillips  thinks  that  the  smaller  herd  is  not  maintain- 
ing itself,  and  that  the  larger  one,  under  apparently 
less  favorable  conditions  as  regards  available  area  of 
range,  is  at  approximately  the  lower  limit  for  keep- 
ing up  its  own  numbers.  He  estimates  that  an  ele- 
phant herd  of  about  twenty-five  individuals  could 
maintain  itself  in  an  unrestricted  range  providing 
civilized  man  were  absent. 

He  gave  us  a  second  example,  of  a  herd  of  some 
three  hundred  springbok  on  a  protected  reserve  of 
six  thousand  acres  in  the  Transvaal,  which  was  un- 
able to  maintain  its  numbers  and  became  reduced 
to  eighty  or  ninety,  on  its  way  toward  total  ex- 
tinction. 

It  is  well  known  that  in  the  life  of  equatorial 
Africa  the  tsetse  fly  plays  an  important  part.  It  carries 
the  trypanosomes  which  cause  the  deadly  disease, 
"sleeping  sickness,"  of  man  and  his  domestic  animals, 
and  which  affect  native  game  as  well.  The  British 


AGGREGATIONS  OF   HIGHER  ANIMALS  lOQ 

colonial  governments  have  been  active  in  attempts 
to  control  the  density  of  these  fly  populations.  In 
general  they  are  restricted  to  damp,  low-lying  forest. 
In  districts  where  this  is  confined  to  the  borders  of 
water-courses,  and  hence  where  the  fly  belt  has  nat- 
urally a  definite  limit  and  is  restricted  in  size,  an 
ingenious  fly  trap  has  been  used  successfully.  The 
trap  takes  advantage  of  the  natural  reactions  of  the 
tsetse  fly.  These  are  strongly  positive  to  a  slightly 
moving  dark  object  a  few  feet  above  ground.  With 
appropriate  screening  they  can  be  caught  as  they  fly 
toward  such  an  object;  they  will  fly  up  and  fall  back 
until  they  literally  wear  themselves  out.  It  was  at 
first  thought  that  such  a  trap  would  be  helpful  chiefly 
in  reducing  the  excess  fly  population;  then,  to  the 
delight  of  the  control  officials,  they  found  that  when 
in  these  restricted  fly  belts  the  tsetse  flies  had  been 
trapped  down  to  a  certain  minimum  population 
there  was  no  need  to  catch  the  very  last  flies;  below 
the  minimum  level  those  remaining  disappeared 
spontaneously  from  the  area.  Nor  did  they  return 
unless  brought  back  in  considerable  numbers  accom- 
panying movements  of  game,  or  as  a  result  of  the 
slow  extension  of  range  from  other  infested  areas. 
The  work  of  the  control  officials  in  such  regions  thus 
was  very  much  easier  than  had  been  anticipated. 
Two   pertinent   cases    concerning    the    minimum 


no  THE  SOCIAL  LIFE  OF  ANIMALS 

number  below  which  a  species  cannot  go  with  safety 
have  come  in  part  under  my  own  observation.  In 
1913,  my  first  summer  at  the  Marine  Biological  Lab- 
oratory at  Woods  Hole,  Massachusetts,  the  veteran 
scientists  of  the  laboratory,  at  least  those  who  still 
were  willing  to  exhibit  naturalistic  enthusiasms,  were 
greatly  pleased  at  the  visit  of  a  flock  of  laughing  gulls 
to  the  Eel  Pond  near  the  laboratory.  The  main 
breeding  ground  of  these  gulls  is  on  Muskeget  Island 
off  Nantucket.  In  1850  the  laughing  gulls  were  abun- 
dant there;  but  they  were  exposed  to  the  depreda- 
tions of  egg  takers  and  later,  about  1876,  to  the 
attacks  of  men  interested  in  obtaining  their  striking 
wings  and  other  feathers  to  satisfy  the  millinery  de- 
mand for  feathers  of  native  birds,  which  was  then 
at  its  height.  (49)  Under  this  slaughter  the  colony 
was  nearly  wiped  out;  at  its  low  point  about  1880 
there  were  not  more  than  twelve  pairs  of  laughing 
gulls  left  on  Muskeget  Island,  and  only  a  few  of  these 
bred.  A  warden  was  employed  in  a  somewhat  extra- 
legal capacity  by  certain  ornithologists  who  regretted 
seeing  the  species  die  out,  and  he  was  assisted  by  the 
captain  of  the  local  life-saving  crew  in  protecting  the 
gulls  from  raids.  Later  changes  in  laws  regarding 
protection  of  birds  and  the  use  of  plumage  in  mil- 
linery gave  more  secure  protection  for  the  growing 
colony.  For  the  first  ten  years  the  birds  increased 


AGGREGATIONS   OF   HIGHER  ANIMALS  111 

slowly,  but  thereafter  more  rapidly,  until  there  are 
now  thousands  breeding  on  the  island,  and  their 
range  has  spread  to  the  mainland.  In  Woods  Hole,  at 
the  present  time,  these  birds  whose  return  in  1913 
excited  so  much  comment  are  as  common  as  the 
terns.  In  this  case,  a  few  breeding  pairs,  nesting  in  a 
relatively  safe  place,  were  able  to  regenerate  the  local 
population  in  less  than  fifty  years;  all  that  was  needed 
was  protection  from  the  predations  of  man. 

The  nesting  colonies  of  gulls  have  attracted  atten- 
tion from  many;  a  report  by  Darling  has  recently 
appeared  concerning  certain  relations  between  num- 
bers of  herring  gulls  in  a  colony  and  breeding  be- 
havior, and  survival  of  young  gulls  on  Priest  Island 
off  the  northwest  coast  of  Scotland.  (39)  There  are 
indications  that  the  members  of  larger  colonies  stim- 
ulate each  other  to  begin  mating  activities  earlier 
than  when  the  colonies  are  smaller  and,  what  is 
apparently  more  important,  there  tends  to  be  a 
shorter  spread  in  the  time  from  the  laying  of  the  first 
egg  until  the  last  one  is  laid.  This  means  that  the 
breeding  activities  are  more  intense  while  they  last. 

The  period  between  hatching  and  the  growth  of 
the  first  adult  plumage  is  a  crucial  time  in  the  life 
of  young  gulls.  While  they  are  in  the  downy  stage 
they  are  preyed  upon  by  outside  predators;  also  at 


112 


THE  SOCIAL  LIFE  OF  ANIMALS 


this  time  the  gull  chicks  that  wander  from  their  home 
nests  may  be  pecked  to  death  by  other  members  of 
the  colony.  The  toll  of  the  chicks  is  comparatively 
less,  the  shorter  the  time  from  the  hatching  of  the 


Survivor) 


Time 


Fig.  i8.  The  "spread"  of  time  in  which  eggs  are  laid 
in  a  colony  of  herring  gulls  affects  the  percentage  that 
survive.  The  smaller  the  colony  the  longer  the  spread, 
and  the  fewer  survivors.  [From  Darling  (39)  by  permis- 
sion of  The  Macmillan  Co.] 

first  fuzzy  young  gull  until  the  last  one  changes  to 
a  young  fledgling  with  adult  feathers.  These  relations 
are  graphically  shown  in  Figure  18. 

Darling  thinks  that  the  greater  success  of  the  larger 
colonies  does  not  lie  in  any  vague  factor  of  mutual 
protection,  but  in  the  nearer  approach  to  simultane- 
ous breeding  throughout  the  colony.  This  is  a  phase 
of  social  facilitation  which  will  be  discussed  more 
fully  in  a  later  chapter. 

These  observations  need  to  be  extended  and  con- 


AGGREGATIONS  OF   HIGHER  ANIMALS  1  I  3 

firmed.  They  suggest  one  mechanism,  that  of  mutual 
stimulation  to  mating,  which  may  have  operated  to 
produce  social  nesting  among  birds,  and  which  seems 
capable  of  giving  added  survival  value  to  the  larger 
colonies,  once  the  habit  of  collecting  into  breeding 
flocks  is  established.  We  have  here  a  suggestion  that 
these  social  colonies  of  birds  have  evolved  far  enough 
so  that  there  has  come  to  be  a  threshold  of  numbers 
below  which  successful  mating  does  not  take  place. 
The  numbers  that  constitute  this  threshold  probably 
vary  under  a  variety  of  conditions. 

In  one  case,  when  only  two  pairs  were  present, 
nests  were  built  but  no  eggs  were  laid,  while  in  a 
more  favorable  season,  with  three  pairs,  eggs  were 
laid  and  one  chick  out  of  eight  that  hatched  lived 
through  the  downy  stage. 

I  saw  the  laughing  gulls  myself  at  Woods  Hole 
last  summer;  and  I  also  found  a  paper  by  Gross  giv- 
ing the  case  of  another  almost  extinct  population 
which  could  not  be  revived.  The  heath  hen,  prob- 
ably a  representative  of  an  eastern  race  of  the  prairie 
chicken,  was  formerly  very  abundant  in  Massachu- 
setts, and  may  have  been  distributed  from  Maine  to 
Delaware,  or  perhaps  even  further  south.  It  was  grad- 
ually isolated  by  the  killing  of  birds  in  the  intermedi- 
ate region  and  was  driven  back,  until  about  1850  it 
was  found  only  on  Martha's  Vineyard  and  the  near-by 


114  THE  SOCIAL   LIFE  OF   ANIMALS 

islands,  and  among  the  pine  barrens  of  New  Jersey. 
(56)  By  1880,  except  for  attempted  and  unsuccessful 
introductions  elsewhere,  it  was  probably  restricted  to 
Martha's  Vineyard.  In  1890-92  it  was  estimated  that 
one  hundred  to  two  hundred  birds  remained  on  that 
island.  Then  several  things  happened  at  about  the 
same  time:  prairie  chickens  were  introduced  and 
probably  interbred  with  the  vanishing  heath  hen, 
protection  of  the  birds  was  stiffened,  and  collectors' 
prices  went  up!  It  is  an  interesting  commentary  that 
most  of  the  museum  specimens,  of  which  208  are 
known  at  present,  were  collected  between  1891  and 
1900,  when  the  probable  extinction  of  the  heath  hen 
was  noised  abroad.  This  is  one  of  the  modern  handi- 
caps of  small  numbers;  let  a  species  or  race  become 
known  to  be  rare,  and  museum  collectors  feel  it 
their  special  duty  to  get  a  good  supply  laid  in,  just 
in  case  it  does  become  extinct. 

By  1907,  when  the  Heath  Hen  Association  was 
formed  and  employed  a  competent  warden,  the  count 
had  been  reduced  to  seventy-seven.  Massachusetts 
became  aroused  and  purchased  six  hundred  acres  of 
heath  hen  range  and  leased  a  thousand  acres  more. 
The  reservation  was  near  a  state  forest  which  added 
another  thousand  acres  of  protected  range.  The  birds 
responded  to  increased  care  and  by  1916  it  was  esti- 
mated that  there  were  two  thousand  in  existence. 


AGGREGATIONS   OF   HIGHER  ANIMALS  11 5 

Then  came  a  fire,  a  gale,  and  a  hard  winter,  with 
an  unprecedented  flight  of  goshawks,  and  in  April, 
1917,  there  were  fewer  than  fifty  breeding  pairs.  The 
next  year,  when  there  was  an  estimated  total  popu- 
lation of  150,  the  heath  hen  range  was  invaded  by 
several  expert  photographers  who  took  motion  pic- 
tures of  mating  behavior.  In  the  face  of  this  disturb- 
ance at  a  critical  time,  still  a  good  year  allowed  the 
birds  to  increase  and  again  to  spread  over  Martha's 
Vineyard.  In  1920,  314  were  counted;  but  thereafter 
a  decline  in  numbers  set  in  which  was  never  stopped. 
The  figures  for  those  five  successive  years  are:  117, 
100,  28,  54,  25.  At  this  point  extra  wardens  were  put 
on  the  job,  who  killed  more  cats,  crows,  rats,  hawks, 
and  owls,  the  enemies  of  the  heath  hen.  The  next 
year's  count  was  35;  in  1927,  there  were  20;  but  in 
1928,  in  a  census  that  lasted  four  days,  only  a  single 
male  was  found.  No  other  bird  was  seen  thereafter, 
though  a  reward  of  a  hundred  dollars  was  offered 
for  the  discovery  of  another.  This  single  male  was 
banded  and  released  and  was  last  seen  alive  on  Febru- 
ary 9,  1932.  With  his  death  the  heath  hen  became 
extinct.  (18) 

When  this  much  is  known  of  the  decline  in  num- 
bers of  a  given  species  there  should  be  some  knowl- 
edge of  the  factors  involved  in  its  extinction.  There 
is.  In  the  earlier  years,  as  I  have  indicated  with  re- 


Il6  THE  SOCIAL  LIFE  OF  ANIMALS 

gard  to  museum  collecting,  there  was  undoubtedly  a 
considerable  amount  of  poaching;  but  as  population 
of  heath  hens  declined,  local  sentiment  turned  in 
favor  of  protection  and  poaching  decreased,  both 
because  of  a  more  intelligent  public  reaction  to  the 
birds,  and  because  of  closer  patrol  by  wardens.  Dr. 
Gross,  whose  account  I  have  been  following,  thinks 
that  there  was  evidence  of  an  inadaptability  of  the 
species,  an  excessive  inbreeding,  and,  at  the  end,  an 
excessive  number  of  males.  In  such  small  populations 
the  sex  ratios  frequently  become  highly  abnormal. 
Disease  and  parasites  took  their  toll.  Predators,  par- 
ticularly cats  and  rats,  were  active.  The  females  hid 
their  nests  well  and  were  faithful  in  remaining  on 
them,  so  that  they  were  killed  off  by  the  fires  which 
at  times  whipped  over  the  breeding  grounds. 

Over  sixty  thousand  dollars  was  spent  in  trying  to 
save  the  heath  hen,  but  without  success.  In  contrast 
to  the  laughing  gull,  which  nested  in  a  relatively 
safe  place  and  which  came  back  from  a  population 
as  low  as  the  heath  hen's  until  the  very  last,  this 
unfortunate  species  was  not  able  to  adjust  itself  and 
continue  existence,  even  with  as  intelligent  human 
help  as  could  be  mustered  in  its  favor. 

The  general  conclusion  seems  to  be  that  different 
species  have  different  minimum  populations  below 


AGGREGATIONS  OF   HIGHER  ANIMALS  1  1 7 

which  the  species  cannot  go  with  safety,  and  that  in 
some  instances  this  is  considerably  above  the  theo- 
retical minimum  of  one  pair. 

By  way  of  the  laboratory,  the  coastal  regions  of 
Massachusetts,  and  South  African  grassland  and  for- 
est, we  are  arriving  at  a  general  biological  principle 
regarding  the  importance  of  numbers  present  on  the 
growth,  survival  and,  as  we  shall  see,  upon  the  evolu- 
tion of  species  of  animals. 

Lacking  definitive  information  on  this  last  phase 
of  the  subject,  we  shall  turn  to  mathematical  explo- 
rations of  its  possibilities,  as  made  primarily  by  Pro- 
fessor Sewall  Wright.  (127,  41)  Although  the  ideas  to 
be  presented  are  essentially  simple  in  principle,  they 
are  sufficiently  novel  and  unfamiliar  to  challenge  the 
closest  attention. 

I  shall  not  indulge  here  in  the  details  of  the  mathe- 
matical analyses,  for  the  very  good  reason  that  I  do 
not  understand  them.  If  I  were  not  convinced,  how- 
ever, that  Professor  Wright  does  understand  them  I 
should  not  present  this  outline.  It  is  only  fair  to  say 
that,  in  my  opinion,  in  dealing  with  these  ideal  popu- 
lations Professor  Wright  cannot  bring  into  sharp 
focus  at  one  time  all  the  factors  that  may  be  acting 
in  nature.  This  is  what  he  Has  been  courageous 
enough  to  attempt;  the  more  nearly  he  succeeds,  the 
more  likely  is  the  calculation  to  be  too  complex  for 


1  1  8  THE  SOCIAL   LIFE   OF  ANIMALS 

presentation  in  detail  except  to  highly  specialized 
readers. 

The  environment  is  in  a  state  of  constant  flux  and 
its  progressive  changes,  whether  slow  or  fast,  make 
the  well-adapted  types  of  the  past  generations  into 
misfits  under  present  conditions.  The  result  may  be 
rectified  either  by  the  extinction  of  the  species,  if  it 
is  not  sufficiently  plastic,  or  through  reorganization 
of  the  hereditary  types.  In  such  a  reorganization  the 
simple  Lamarckian  reactions  apparently  do  not  op- 
erate; that  is  to  say,  when  confronted  with  new, 
critical  conditions,  species  cannot  go  to  work  and 
produce  needed  changes  to  order.  The  reactions  are 
much  more  complicated  than  that. 

To  present  the  modern  interpretation  of  this  re- 
organization I  need  three  technical  terms  which  I 
shall  define  before  using.  Genes  are  bits  of  proto- 
plasm too  small  to  be  seen  through  the  microscope, 
which  are  located  in  all  cells  and  which  are  thought 
to  be  the  bearers  of  heredity.  They  behave  as  indi- 
visible units,  that  is  to  say,  a  gene  if  present  in  an 
organism  is  either  transmitted  as  a  whole  or  not  at 
all.  Gene  frequency  is  the  term  applied  to  the  fre- 
quency with  which  a  given  gene  is  found  in  a  popu- 
lation, relative  to  the  total  possible  frequency  (two 
in  every  individual).  By  mutation  is  meant  a  large  or 
small    hereditary   change    which    appears    suddenly, 


AGGREGATIONS   OF   HIGHER  ANIMALS  IIQ 

usually  in  the  sense  in  which  I  shall  use  it,  as  a  result 
of  a  change  in  one  or  more  genes.  With  these  three 
terms  in  mind  we  are  ready  to  try  to  understand  how 
the  hereditary  types  may  become  reorganized. 

Such  a  reorganization  implies  a  change  in  gene 
frequencies.  By  this  I  mean  now  that  there  will  be  a 
decrease  in  the  abundance  of  the  genes  which  were 
responsible  for  the  past  adaptations  that  are  now 
obsolete,  and  an  increase  in  the  frequency  of  those 
genes  which  allow  an  adaptation  to  the  new  condi- 
tions. Gene  frequencies  remain  constant  in  a  large 
population  unless  changed  by  mutation,  selection  or 
immigration.  This  is  because  of  the  unitary  charac- 
ter, without  blending,  and  the  symmetry  of  the 
Mendelian  mechanism  of  heredity. 

These  life-saving  genes  may  have  been  present 
in  the  species  for  a  million  years  as  a  result  of 
long  past  mutations,  without  having  been  of  any 
value  to  the  species  in  all  that  time.  Now  under 
changed  conditions  they  may  save  it  from  extinction. 
It  is  important  to  note  that  organisms  do  not  usually 
meet  changed  conditions  by  waiting  for  a  new  muta- 
tion; frequently  all  members  of  a  species  would  be 
dead  long  before  the  right  change  would  occur.  This 
means  that  since  a  species  cannot  produce  adaptive 
changes  when  and  where  needed,  in  order  to  persist 


120  THE  SOCIAL  LIFE  OF  ANIMALS 

successfully  it  must  possess  at  all  times  a  store  of 
concealed  potential  variability. 

I  may  interject  parenthetically  that  at  times  this 
appears  to  call  for  the  presence  of  a  considerable 
number  of  individuals  as  a  necessary  condition  to 
provide  the  needed  variations.  A  part  of  this  reserve 
of  variability  may  be  of  no  use  under  any  circum- 
stances; some  characters  may  be  useful,  some  may 
never  meet  with  the  circumstances  under  which  they 
would  have  survival  value;  while  others,  though  of 
no  use  or  even  harmful  when  they  appear,  may  later 
enable  the  species  to  live  under  newly  changed  con- 
ditions. 

Hereditary  changes  tend  to  be  eliminated  as  soon 
as  they  run  counter  to  decided  environmental  selec- 
tion. In  large  populations  the  results  of  mutations 
tend  to  stabilize  about  some  average  gene  frequency, 
which  represents  the  interaction  between  the  rate  of 
mutation  and  the  degree  of  selection.  Frequently 
mutation  pressure  pushes  in  one  direction  and  selec- 
tion in  another  and  the  resulting  gene  frequency  in 
the  population  represents  a  point  or  zone  of  equi- 
librium between  these  forces.  In  small  populations 
which  are  not  too  small,  selection  between  genes 
becomes  relatively  ineffective,  and  the  gene  fre- 
quencies drift  at  random  over  a  wide  range  about  a 
certain  mean  position.  In  very  small  breeding  popu- 


AGGREGATIONS  OF   HIGHER  ANIMALS 


121 


lations,  even  though  these  may  be  small  isolated 
colonies  of  a  large  widespread  species,  gene  fre- 
quencies drift  into  fixation  of  one  alternative  or  an- 
other more  rapidly  than  they  are  changed  by  selec- 


CHANCE 
I 


0.5 


LOO 


Fig.  19.  In  small  populations,  genes  drift  into  fixa- 
tion or  loss  largely  irrespective  of  selection;  the  fre- 
quency of  fixation  or  loss  depends  in  the  long  run  on  the 
relative  frequency  of  mutation  and  reverse  mutation. 
(After  Wright.) 

tion  or  by  mutation.  Mutation,  however,  prevents 
permanent  fixation.  The  condition  at  any  given 
moment  is  largely  a  matter  of  chance. 

Perhaps  a  diagram  will  help  at  this  point.  In  Fig- 
ure 19  the  horizontal  axis  shows  the  different  gene 
frequencies  in  a  population,  and  the  vertical  axis 
gives  the  chances  of  the  population  under  considera- 
tion possessing  any  given  gene  frequency.  At  the  left, 


122  THE   SOCIAL   LIFE   OF  ANIMALS 

the  gene  frequency  is  zero;  that  is,  the  gene  in  ques- 
tion is  absent  from  the  population  for  the  time  being. 
The  height  of  the  curve  shows  that  there  is  a  good 
chance  of  this  happening.  At  the  extreme  right  the 
gene  has  become  fixed  and  all  animals  in  the  popu- 
lation have  it;  they  are  a  pure  culture  so  far  as  this 
gene  is  concerned.  Again  there  is  a  high  degree  of 
probability  that  this  may  happen  when  numbers  are 
few.  But  the  intermediate  condition,  when  the  gene 
is  present  in  some  but  not  all  of  the  animals,  shows 
little  chance  of  occurrence. 

In  such  small  populations,  as  has  been  said  before, 
the  gene  frequency  is  determined  mainly  by  chance; 
any  given  hereditary  unit  tends  to  disappear  com- 
pletely or  become  fixed  and  occur  in  all  members  of 
the  small  inbreeding  colony.  Such  a  condition  may 
have  been  reached  in  the  inbred  population  of  the 
heath  hen  on  Martha's  Vineyard. 

With  populations  that  are  intermediate  in  size 
there  is  a  greater  variety  of  possibilities.  Some  genes 
are  lost,  others  reach  chance  fixations,  and  others 
fluctuate  widely  in  frequency  from  time  to  time. 
These  conditions  are  shown  in  Figure  20. 

If  a  given  species  is  isolated  into  breeding  colonies 
in  such  a  way  that  but  little  emigration  occurs  be- 
tween them,  a  condition  known  to  exist  in  nature,  in 
the  course  of  time,  as  Professor  Wright  shows,  the 


AGGREGATIONS   OF   HIGHER  ANIMALS  123 

species  will  become  divided  into  local  races.  This 
will  happen  although  at  the  time  of  separation  the 
populations  were  all  homogeneous  and  the  environ- 
ment of  all  remains  essentially  similar. 

If  the  environment  does  remain  steady  the  larger 


SELECTION 

4 

HUTATIOrt  MUTATIOM 

CHANCE 


0  0.5  100 

Fig.  20.  In  medium  populations,  gene  frequencies 
drift  at  random  about  an  intermediate  point  but  not  so 
much  so  that  complete  fixation  or  loss  is  likely  to  occur. 
(After  Wright.) 

colonies  will  tend  to  keep  the  same  hereditary  consti- 
tution as  that  which  the  whole  species  formerly  had. 
(Figure  21.)  Small  breeding  colonies  will,  how- 
ever, become  pure  cultures  for  different  characters, 
and  it  is  impossible  to  predict  the  course  of  the 
hereditary  drift  in  any  of  these  populations.  As  illus- 
trated in  Figure  20,  the  fixation  will  be  a  matter  of 
chance,  and  local  races  will  result  without  any  neces- 
sary reference  to  adaptation. 

The  snails  in  the  different  mountain  valleys  of 
Hawaii  afford  the  classical  illustration  of  this  point. 


124 


THE   SOCIAL   LIFE   OF   ANIMALS 


Each  individual  mountain  valley  has  its  separate 
species  of  snails.  They  are  distinguished  by  size,  by 
color  markings,  and  by  other  characters  which  may 
be  wholly  non-adaptive. 

Colonies  which  are  intermediate  in  size  will  pre- 


UTATION 

CHANCE 

A 


I 


0  0.5  1.00 

Fig.  21.  In  large  populations,  gene  frequency  is  held 
to  a  certain  equilibrium  value  as  a  result  of  the  oppos- 
ing pressures  of  mutation  and  selection.  (After  Wright.) 

serve  a  part  of  the  variability  that  will  be  lost  in  the 
smaller  colonies.  Even  so,  there  will  be  some  inde- 
pendent drifting  apart  of  the  various  gene  frequen- 
cies, so  that  these,  too,  will  give  rise  to  new  local 
races.  Professor  Wright's  calculations  show  that  with 
mutation  rates  of  the  order  of  i:io,ooo  or  1:100,000, 
such  intermediate  populations,  optimal  for  evolution, 
will  consist  of  some  thousands  or  tens  of  thousands  of 
individuals. 

With  small  breeding  populations,  then,  genes  tend 
to  become  fixed  or  lost.  Even  rather  severe  selection 


AGGREGATIONS   OF   HIGHER  ANIMALS  125 

is  without  effect.  Individual  genes  drift  from  one 
state  of  fixation  to  another  regardless  of  selection.  In 
large  populations,  gene  frequencies  tend  to  come  to 
equilibrium  between  mutation  and  selection,  and  if 
selection  is  severe,  there  tends  to  be  a  fixation  of  the 
gene  or  genes  that  carry  adaptive  modifications,  and 
evolution  comes  to  a  standstill. 

With  a  population  intermediate  in  size,  when  there 
are  enough  animals  present  to  prevent  fixation  of 
the  genes  on  the  one  hand,  but  on  the  other,  not 
enough  animals  to  prevent  a  random  drifting  about 
the  mean  values  determined  by  selection  and  muta- 
tion, then  evolution  may  occur  relatively  rapidly. 
The  results  obtained  will  depend  upon  the  balance 
between  mutation  rate,  selection  rate,  and  the  size 
of  the  effective  breeding  population. 

In  one  more  case  the  effect  of  differences  in  sever- 
ity of  selection  was  worked  out  by  Professor  Wright 
(Figure  22).  With  a  moderate  mutation  rate,  if  the 
selection  is  relatively  weak,  mutation  pressure  may 
determine  the  result  and  the  given  character  will 
then  drift  to  fixation  or,  as  shown  in  the  diagram,  to 
extinction.  As  selection  pressures  increase,  selection 
tends  to  take  charge  of  the  end  products,  and,  if 
slight,  there  is  a  wide  variation  about  a  mean;  if 
more  intense,  the  amount  of  variation  becomes  less 
and  less. 


126 


THE   SOCIAL   LIFE   OF  ANIMALS 


When  a  species  is  broken  up  into  different  breed- 
ing colonies,  as  it  is  with  the  snails  in  the  Hawaiian 


fN5=80 


Fig.  22.  As  intensity  of  selection  increases  it  becomes 
more  and  more  dominant  in  determining  the  end  result, 
and  the  degree  of  variation  is  lessened;  4Ns  gives  selec- 
tion pressure.  (From  Wright.) 

valleys,  (57)  it  can  be  similarly  shown  that  the  effects 
produced  depend  on  the  rate  of  emigration  between 
colonies,  as  well  as  selection  pressure,  mutation  pres- 
sure, and  population  size,  other  factors  being  con- 
stant. Cross-breeding  introduces  genes  into  a  popula- 


AGGREGATIONS   OF   HIGHER  ANIMALS  127 

tion  in  a  way  that  is  essentially  identical  with  muta- 
tion in  its  mathematical  consequences;  however, 
similar  results  may  be  obtained  in  a  much  shorter 
time  by  cross-breeding.  And  in  fact  all  the  different 
results  which  have  just  been  illustrated  can  be  dupli- 
cated by  varying  the  numbers  of  the  emigrants. 

This  is  not  the  place  to  explore  all  the  implica- 
tions and  possibilities  of  these  interesting  analyses. 
The  highly  significant  conclusion  has  been  reached 
that  if  a  species  occurs  not  as  a  single  breeding  unit 
but  broken  into  effective  breeding  colonies  which 
are  almost  isolated  from  each  other,  the  members  of 
different  colonies,  given  sufficient  vigor,  may  evolve 
into  dissimilar  local  races.  If  one  of  these  becomes 
well  adapted  to  its  environment  it  may  increase  in 
numbers  and  send  out  numerous  emigrants.  If  these 
emigrants  find  and  interbreed  with  members  of  other 
less  advanced  colonies  they  will  grade  these  up  until 
they  resemble  the  most  adapted  colony.  This  part  of 
the  process  resembles  a  stock  breeder's  grading  up 
of  a  mediocre  herd  of  cattle  by  repeated  infusions  of 
new  and  improved  ''blood"  into  his  herd.  The  sig- 
nificant thing  here  is  that  the  random  differentiation 
of  local  populations  furnishes  material  for  the  action 
of  selection  on  types  as  wholes,  rather  than  on  the 
mere  average  adaptive  effects  of  individual  genes. 

The  end  results  will  vary  even  when  the  original 


128  THE  SOCIAL   LIFE   OF  ANIMALS 

population  was  homogeneous,  and  when  mutation 
rates  are  similar  throughout,  even  though  selection  is 
in  the  same  direction  in  all  parts  of  the  different 
colonies.  The  primary  factor  under  these  conditions 
will  be  that  of  effective  breeding  population  size,  and 
there  will  be  greater  chance  for  varied  evolution 
among  the  populations  that  are  intermediate  in  size, 
as  contrasted  with  those  which  are  small  or  large,  and 
still  greater  chance  for  evolution  when  a  large  species 
is  broken  into  small  breeding  colonies  which  are  not 
completely  isolated  from  each  other. 

This  argument,  even  as  I  have  simplified  it,  is  not 
too  easily  followed  the  first  time  one  goes  over  it. 
Perhaps  my  use  of  an  old  teaching  trick,  that  of  repe- 
tition of  the  same  ideas  with  different  words  and 
different  illustrations,  may  be  forgiven.  In  doing  so 
I  am  still  leaning  heavily  on  Professor  Wright.  The 
series  of  diagrams  shown  in  Plate  IV  are  built  on 
one  fundamental  background.  In  perspective  we  see 
two  elevations,  one  higher  than  the  other,  and  two 
depressions  which  are  the  low  points  in  a  valley 
between  the  two  peaks.  Every  position  is  intended 
to  represent  a  different  combination  of  gene  fre- 
quencies. The  peaks  represent  gene  combinations 
which  are  highly  adaptive;  the  depressions  represent 
those  that  lack  adaptive  value.  The  degree  of  adap- 
tiveness  is  shown  by  the  height  occupied  by  the  given 


I# 


€ 

o^ 

.X-  O 


clI 


PLATE  IV.  A  population  originally  possessed  a  set 
of  gene  combinations  of  some  slight  adaptive  value 
(dotted  line).  With  increased  mutation  rate  it  can  ex- 
pand to  less  adapted  levels  (A);  with  increased  selec- 
tion it  contracts  (B);  if  the  environment  changes  the 
gene  frequency  must  shift  (C);  with  small  numbers 
and  close  inbreeding  the  course  of  evolution  is  erratic 
and  extinction  usually  follows  (D);  with  larger  num- 
bers, evolution  takes  place  more  readily  (E);  most  read- 
ily, when  a  large  population  is  broken  into  local 
colonies  with  inter-emigiation  (F).  (Modified  from 
Wright.) 


AGGREGATIONS   OF   HIGHER  ANIMALS  129 

population.  The  variability  of  the  population  is 
shown  by  the  size  of  the  area  that  is  occupied.  Every 
individual  in  a  species  may  have  a  different  gene 
combination  from  every  other,  and  yet  the  species 
may  occupy  a  small  region  relative  to  all  the  possi- 
bilities. 

We  may  call  the  lower  peak  Mount  Minor  Adap- 
tation and  the  higher  one  Mount  Major  Adaptation. 
In  Figure  A  we  find  a  population  which  is  fairly 
well-adapted,  but  not  so  much  so  as  if  it  occupied  the 
higher  peak.  Its  original  position  and  its  variability 
are  shown  by  the  dotted  circle.  As  a  result  of  increased 
rate  of  mutation  or  of  reduced  selection,  or  both,  the 
variability  of  the  population  has  increased  and  it 
now  spreads  down  to  lower  positions  on  this  Mount 
Minor  Adaptation.  It  contains  more  aberrant  indi- 
viduals and  even  freaks  than  when  subject  to  less 
frequent  mutation  or  to  more  severe  selection,  and  a 
freak  may  appear  that  is  more  adaptive;  but  this 
important  end  has  been  achieved  at  the  expense  of 
the  variability  which  might  have  made  a  major  ad- 
vance possible. 

Figure  C  introduces  a  different  situation.  As  a 
result  of  environmental  change  Mount  Minor  Adap- 
tation has  disappeared  and  the  adapted  population 
has  been  able  to  move  to  a  new  location  at  about  the 
same  level  formerly  occupied;  now  it  is  on  the  slope 


130  THE   SOCIAL   LIFE   OF  ANIMALS 

of  Mount  Major  Adaptation,  and  if  selection  con- 
tinues may  be  expected  to  move  up  that  adaptive 
peak.  A  continually  changing  environment  is  un- 
doubtedly an  important  factor  in  evolution. 

The  effects  of  population  size  are  illustrated  in  the 
next  three  diagrams.  The  general  background  is  the 
same  as  in  Figures  A  and  B.  In  Figure  D  is  shown 
the  effect  of  a  decided  reduction  in  population  size, 
and  consequently  in  variability,  in  the  species  that 
formerly  occupied  Mount  Minor  Adaptation.  It  is 
in  fact  so  small  that  selection  has  become  ineffective 
and  the  different  hereditary  qualities  shift  to  chance 
fixations.  As  non-adaptive  characters  become  fixed  at 
random  the  species  moves  down  from  its  peak  over 
an  erratic,  unpredictable  path.  With  reduction  of 
population  size  below  a  certain  minimum,  control  by 
selection  between  genes  disappears  to  such  an  extent 
that  the  end  can  only  be  extinction. 

With  the  species  population  intermediate  in  size, 
with  the  same  mutation  and  selection  rates  as  before, 
gene  frequencies  move  about  at  random  but  without 
reaching  the  degree  of  fixation  found  in  the  preced- 
ing case.  Since  it  will  be  easier  to  escape  from  low 
adaptive  peaks,  the  population  will  tend  finally  to 
occupy  the  more  adapted  levels.  The  rate  of  progress 
is,  however,  extremely  slow. 

Finally,  in  Figure  F,  we  see  the  case  of  a  large 


AGGREGATIONS   OF   HIGHER  ANIMALS  13I 

species  which  has  become  broken  up  into  many  small 
local  races,  perhaps  as  a  result  of  restricted  environ- 
mental niches.  Each  of  these  local  races  breeds  largely 
within  its  own  colony,  but  there  is  an  occasional  emi- 
gration from  one  to  another.  Each  tends,  if  it  is  small 
in  number,  to  give  rise  to  different  variations  which 
shift  about  in  a  non-adaptive  manner.  The  total 
number  of  relatively  stable  variations  will  be  much 
greater  since  the  total  number  of  individuals  is  so 
much  larger  than  in  E.  Under  these  conditions  the 
chances  are  good  that  some  of  the  local  colonies  will 
escape  from  the  influence  of  Mount  Minor  Adapta- 
tion and  manage  to  cross  the  valley  to  Mount  Major 
Adaptation.  Here  the  race  will  expand  in  numbers 
and  will  send  out  more  and  more  emigrants  which 
will  interbreed  with  the  stocks  in  the  less  adapted 
colonies  and  tend  to  grade  them  all  up  toward  a 
higher  adaptive  level. 

The  conclusion  is  as  Professor  Wright  says:  "A 
subdivision  of  a  large  species  into  numerous  small, 
partially  isolated  races  gives  the  most  effective  setting 
for  the  operation  of  the  trial  and  error  mechanism 
in  the  field  of  evolution  that  results  from  gene  com- 
binations." 

In  the  rate  of  evolution,  therefore,  population  size 
is  as  important  as  we  have  seen  it  to  be  in  the  growth 


1S2  THE   SOCIAL   LIFE   OF   ANIMALS 

of  individuals  or  in  the  gTO\\ih  of  popnlation  num- 
bers: and  the  optimal  population  size  does  not  coin- 
tide  \sith  either  the  largest  or  smallest  possible  but 
lies  at  some  iiuermediate  point. 


V. 


Group  Behavior 


IN  THE  second  chapter  I  told  of  how  I  stumbled  on 
the  fact  that  in  the  breeding  season  the  normal  be- 
havior of  isopods  is  affected  by  numbers  present. 
Such  effects  have  long  been  known  for  many  types 
of  behavior,  and  it  would  not  be  profitable  here  to 
catalogue  and  analyze  all  the  cases  that  are  on  record. 
Rather,  as  before,  I  shall  select  certain  well-authenti- 
cated examples  of  breeding  reactions  and  of  other 
types  of  behavior.  Those  which  are  chosen  are  espe- 
cially noteworthy  because  of  the  behavior  pattern 
which  is  involved,  or  because  freshly  observed,  or 
both. 

And  here  is  a  shift  in  emphasis.  I  have  been  stress- 
ing the  existence  of  a  widespread,  fundamental  auto- 
matic co-operation  which  has  survival  value,  and  have 
given  evidence  that  it  is  a  common  trait  in  the  animal 
kingdom.  In  this  chapter  I  shall  discuss  group  be- 
havior which  may  or  may  not  have  immediate  sur- 
vival value.  In  each  instance,  and  throughout  the 
discussion  as  a  whole,  I  shall  be  engaged  in  trying 

133 


154  THE  SOCIAL  LIFE  OF  ANIMALS 

to  find  to  what  extent  behavior  is  influenced  by  the 
presence  of  others,  and  shall  not  consistently  attempt 
to  assay  possible  values  which  may  or  may  not  be 
involved. 

With  many  more  or  less  social  animals  the  group 
up  to  a  certain  size  facilitates  various  types  of  be- 
havior. This  is  frequently  called  social  facilitation. 


Shore  Line 

Fig.  23.     Manakin  males  establish  rows  of  mating  courts 
in  the  Panamanian  rain-forest.  (From  Chapman.) 

One  phase  of  social  facilitation  is  illustrated  by  some 
observations  of  the  mature  student  of  birds,  Frank  E. 
Chapman,  (28)  near  the  tropical  laboratory  on  Barro 
Colorado  Island  in  the  rain-forest  of  Panama.  Mr. 
Chapman  found  that  males  of  Gould's  manakin 
establish  lines  of  courting  places  (Figure  23).  The 
manakin  is  a  small  warbler-like  bird,  delicately 
colored  and  relatively  inconspicuous.  Each  of  the 
courting  places  is  occupied  by  a  single  male;  the  line 
thus  formed  extends  for  many  yards  through  the 
undergrowth  of  the  rain-forest.  From  time  to  time 
each  day  during  the  long  nesting  season,  the  males 
resort  to  their  individual  cleared  spots  on  the  forest 


GROUP   BEHAVIOR  1  35 

floor  and  make  their  presence  known  by  a  series  of 
snaps,  whirrs  and  calls  which  may  be  heard  as  far  as 
three  hundred  yards.  The  females,  who  are  more 
quiet  and  retiring,  apparently  are  attracted  by  the 
line  of  males;  they  come  individually  from  the  sur- 
rounding thickets  and  each  mates  with  one  of  the 
males.  The  evidence  suggests  that  they  are  attracted 
from  a  greater  distance  by  the  spaced  aggregation  of 
males  than  they  would  be  by  isolated  courting  places. 
The  more  or  less  organized  line  of  males  in  breeding 
condition  apparently  facilitates  the  mating  of  these 
jungle  birds. 

This  is  a  highly  specialized  example  of  the  wide- 
spread phenomenon  of  territoriality  which  can  be 
recognized  even  among  breeding  fishes,  (103)  and 
which  has  been  much  studied  of  recent  years  in  birds. 
(65)  Typically  the  male  birds  arrive  first  in  the 
spring  and  take  up  fairly  well-defined  territories  in 
the  same  general  area,  which  they  defend  from  in- 
truding males.  Then  the  females  come  in  and  flit 
from  territory  to  territory  before  settling  down  to 
raise  a  brood  with  one  particular  male.  There  is 
always  the  strong  suggestion  that  the  presence  of  a 
number  of  singing  males,  even  if  spaced  about  in 
different  territories,  attracts  and  hastens  the  accept- 
ance of  some  one  of  them  by  an  unmated  female. 

Group  stimulation  of  the  amount  of  food  taken 


136 


THE  SOCIAL  LIFE   OF  ANIMALS 


has  been  reported  for  various  animals,  including 
rats,  (59)  chickens  (23)  and  fishes.  (118)  I  shall  illus- 
trate by  some  of  the  experiments  conducted  in  our 
laboratory   by   Dr.   J.   C.   Welty.   These   have   been 


150 


125 

a 
te. 

s:ioo 


^  75 

< 

< 

o 

u. 

o 

le  25 
la 
<0 

E 

C 


•  GROUPS  OF  FOUR 
O  ISOLATED 


DAILY  FEEDmS   5 


Fig.  24.     Many  kinds  of  fishes  eat  more  if  several  are 
present  than  if  they  are  isolated.  (From  Welty.) 

amply  verified  by  other  research  workers.  In  connec- 
tion with  experiments  on  the  effect  of  numbers  on 
the  rate  of  learning  in  fishes,  which  will  be  discussed 
later.  Dr.  Welty  undertook  to  find  whether  grouped 
fish  ate  more  or  less  than  if  they  were  isolated.  The 
results  of  a  typical  experiment  are  illustrated  in 
Figure  24. 

Goldfish  were  photographed  to  scale,  and  those  of 


GROUP   BEHAVIOR  I37 

similar  size  were  selected  for  experimentation.  Two 
groups  of  four  each  were  placed  in  separate  crystal- 
lizing dishes  and  eight  others  were  isolated  each  into 
a  wholly  similar  dish.  The  different  dishes  were  sep- 
arated by  black  paper  so  that  vision  from  one  to  the 
other  was  impossible.  A  known  number  of  the  small 
crustacean,  Daphnia,  were  introduced  daily  into  each 
dish.  These  living  Daphnia  had  been  screened  so  as 
to  select  the  large  animals  only.  As  shown  by  the  fig- 
ure, fish  in  all  groups  of  four  ate  decidedly  more  on 
the  first  three  days  of  the  experiment.  At  this  time 
the  two  lots  were  shifted.  Those  that  had  been 
grouped  were  now  isolated,  and  vice  versa.  There 
was  an  immediate  shift  in  the  numbers  of  Daphnia 
taken,  with  the  newly  isolated  animals  now  eating 
less  than  the  accompanying  groups.  This  indicates 
that  we  are  dealing  with  an  effect  of  numbers  present 
rather  than  with  chance  differences  in  individual 
appetites.  This  difference  kept  up  steadily  until  the 
last  three  days  of  observation,  when  an  interesting 
complication  arose.  By  this  time  the  grouped  fish 
were  receiving  a  total  of  over  six  hundred  Daphnia 
daily,  including  those  which  were  eaten  and  the 
extras  added  to  insure  an  economy  of  plenty.  Each 
isolated  fish  was  receiving  only  one-fourth  as  many. 
Now  six  hundred  and  more  large  Daphnia,  each 
about  an  eighth  of  an  inch  long,  make  quite  a  swarm 


9,8  THE   SOCIAL   LIFE   OF   ANIMALS 


in  a  none-too-large  crystallizing  dish.  The  consump- 
tion of  food  per  animal  by  the  grouped  fish  fell  off, 
and  as  was  shown  by  appropriate  tests,  this  was  due  to 
the  action  of  a  so-called  confusion  effect.  When  fewer 
Daphnia  were  present,  a  fish  might  be  observed  to 
swim  after  an  isolated  crustacean  and  eat  it,  whereas 
a  dozen  Daphnia  or  so  in  the  immediate  field  of 
vision  seemed  to  offer  conflicting  stimuli  that  blocked 
the  feeding  response.  Working  on  this  suggestion, 
one  group  of  four  was  given  the  usual  quota  of  some 
six  hundred  Daphnia  all  at  once;  another  group  was 
given  only  one  hundred  at  a  time,  and  when  these 
were  approximately  all  eaten  then  another  hundred 
would  fjc  introduced,  and  so  on  until  the  end  of  the 
regular  feeding  period.  This  prevented  the  Daphnia 
from  being  too  dense  at  the  beginning  of  the  hour's 
feeding  time.  The  isolated  fish  were  fed  as  usual. 
Under  these  conditions  the  grouped  goldfish  which 
were  fed  one  hundred  Daphnia  at  a  time  ate  defi- 
nitely more  than  those  given  the  whole  confusing 
mass  at  once. 

Here  we  come  upon  two,  not  one,  mass  effects.  In 
the  first  place  we  see  that  the  fish  in  groups  of  four 
were  stimulated  to  eat  more  food  than  if  isolated, 
and  this  depended  on  their  state  of  aggregation.  But, 
incidental  to  this  demonstration,  we  hnd  that  in  the 
presence  of  too  many  animated  food  particles  a  con- 


GROUP   BEHAVIOR  1  39 

fusion  effect  arises  which  decreases  the  feeding  effi- 
ciency of  the  fish. 

It  has  been  suspected  for  years  that  such  a  confu- 
sion effect  exists  and  has  survival  value  for  small 
animals  flocking  together  in  the  presence  of  a  preda- 
tor, such  as  small  birds  in  the  region  of  a  hawk. 
These  observations  of  Welty's  make  the  best  demon- 
stration that  I  know  of  the  existence  of  such  an 
effect,  in  this  case  the  Daphnia  in  the  presence  of  the 
fish.  I  am  less  interested  in  this  confusion  effect  at 
present  than  in  the  demonstration  of  social  facilita- 
tion in  feeding,  a  phenomenon  which  has  been 
shown  to  exist  for  a  number  of  fishes,  including  zebra 
fish,  paradise  fish,  goldfish  and  guppies  of  the  more 
usual  aquarium  varieties,  and  the  lake  shiner,  No- 
tropis  atherinoideSy  as  well. 

None  of  these  fishes  is  very  social,  that  is,  none 
of  them  group  into  close  schools.  For  evidence  of 
similar  social  stimulation  among  social  animals  it  is 
interesting  to  examine  the  effect  of  numbers  present 
on  the  digging  behavior  of  the  highly  social  ants. 
The  account  of  this  work  was  published  in  1937  by 
Professor  Chen  of  Peiping,  China.  (29) 

These  ants,  a  species  of  Campanotus,  dig  their 
nests  in  the  ground.  It  was  found  that  all  the  worker 
ants  of  this  species  are  capable  of  digging  a  nest 
when  in  isolation,  but  that  the  rate  of  work  varies 


140  THE   SOCIAL   LIFE   OF   ANIMALS 

with  different  individuals.  If  marked  ants,  whose 
reaction  time  has  been  tested  in  isolation,  are  placed 
together  in  pairs  or  in  groups,  they  will  start  work 
sooner  and  will  work  with  greater  uniformity  than 
if  alone. 

With  oriental  patience.  Professor  Chen  and  his 
assistants  collected  and  counted  the  number  of  the 
tiny  pellets  of  earth  which  were  dug  by  different 
individual  ants  when  isolated,  and  when  members 
of  groups  of  two  or  three  ants.  They  found  that  the 
number  of  pellets  removed  is  greater  when  the  ants 
work  in  association  with  others  than  when  each 
works  alone.  This  accelerating  effect  is  greater  for 
slow  than  for  rapid  workers;  when  ants  with  inter- 
mediate working  tendencies  were  tested  (Figure  25) 
they  were  found  to  be  speeded  up  when  in  com- 
pany with  a  rapid  co-worker  and  relatively  retarded 
when  placed  with  a  slowly  working  ant.  Interestingly 
enough,  there  was  no  difference  between  the  stimu- 
lating effect  of  one  additional  ant  and  of  many  ants 
on  the  rate  of  work  of  a  given  individual.  The  social 
facilitation  seemed  maximum  for  these  digging  tests 
when  only  a  second  individual  was  present. 

Ants  which  regularly  work  rapidly  were  found  to 
be  physiologically  different  from  those  that  work 
more  slowly.  The  faster  workers  were  more  suscepti- 
ble to  starvation,  to  drying,  and  to  exposure  to  ether 


0    5    ra   e   20  25  30  35  40  45  50  55  60  5    10   15  20  25  30  35  40  45  50  55  60 
TIME   IS  MINUTES 

Fig.  25.  An  ant  which  works  at  an  intermediate  rate 
(Ml)  may  be  speeded  up  if  placed  with  an  ant  which 
works  more  rapidly  (Rl)  and  slowed  down  if  put  with  a 
slower  worker  (SI).  (From  Chen.) 


142  THE  SOCIAL   LIFE   OF   ANIMALS 

or  to  chloroform.  Tests  that  have  been  made  by 
others  indicate  that  animals  that  are  more  active 
physiologically  usually  succumb  sooner  under  such 
adverse  conditions,  just  as  these  rapidly-working  ants 
were  found  to  do.  These  are  exceedingly  interesting 
results  because  here  we  see  that  ants  with  apparently 
innate  differences  in  speed  of  fundamental  processes 
are  affected  in  their  speed  of  digging  by  the  presence 
or  the  absence  of  a  nest  mate.  The  ant  of  intermediate 
speed,  presumably  with  an  intermediate  underlying 
reaction  system,  is  most  interesting  of  all,  because  it 
can  be  either  speeded  up  or  retarded  according  as  it 
is  placed  with  an  active  or  a  more  passive  individual. 

In  this  connection  it  has  been  known  for  over  a 
decade  scientifically  what  was  common  sense  before 
that  time,  namely,  that  human  animals,  whether 
adults  or  children,  can  accomplish  more  mental  and 
physical  work,  at  least  of  certain  kinds,  and  will  work 
with  greater  uniformity  when  in  association  with 
others  doing  similar  tasks,  than  if  obliged  to  work  in 
isolation.  (15,  84) 

Such  considerations  lead  directly  to  problems  con- 
cerning the  effect  of  numbers  present  on  the  rate  of 
learning  in  man.  Here  we  find  a  set  of  questions  that 
have  great  and  immediate  human  significance.  The 
world  over,  the  training  of  the  young  animals  of 
their  own  species  is  one  of  the  major  preoccupations 


GROUP   BEHAVIOR  143 

of  mankind.  This  is  particularly  true  in  the  United 
States,  where  we  are  engaged  in  mass  education  on 
an  unprecedented  scale.  This  teaching  of  the  young 
to  the  extent  to  which  we  are  attempting  it  is  an 
expensive  business  in  time,  in  effort  and  in  money. 
We  need  to  know,  therefore,  the  number  of  these 
interesting  young  animals  that  can  be  trained  to- 
gether with  best  results.  In  other  words,  what  is  the 
optimal  class  size  for  the  various  levels  of  training 
from  pre-school  days  through  the  preparation  for 
the  doctor's  degree  and  further? 

In  part,  the  proper  answer  to  this  question  calls 
for  a  statement  of  educational  objectives.  The  devel- 
opment of  strong  individuality,  for  example,  is  not 
necessarily  accomplished  by  the  same  teaching  meth- 
ods and  class  size  which  favor  the  growth  of  conform- 
ity to  group  patterns;  and  the  rapid  development  of 
mastery  of  so-called  skills  may  call  for  difiEerent  num- 
ber relations  than  those  needed  for  the  mastery  of 
logical  thought. 

Even  without  positive  information  we  can  guess 
that  the  tutorial  method  with  individuals  or  very 
small  groups  will  best  serve  some  ends  while  others 
will  be  achieved  most  readily  in  larger  groups.  The 
question,  or  a  simplified  part  of  it,  thus  becomes: 
What  class  size  favors  optimal  rate  of  learning  of  the 
usual  class  material  presented  at  different  ages? 


144  THE  SOCIAL  LIFE   OF  ANIMALS 

As  might  be  anticipated,  the  difficulties  of  human 
experimentation  being  what  they  are,  it  is  hard  to 
collect  accurate  information  on  this  point.  Much 
depends  on  the  comparative  accuracy  of  the  sam- 
pling, and  also  on  more  subjective  factors,  such  as 
the  attitude  of  the  teacher  and  of  the  students  toward 
large  and  small  classes.  There  is  also  a  factor  which  I 
have  not  seen  mentioned  in  the  literature  on  the 
subject,  the  effect  on  the  student  of  realizing  or  sus- 
pecting that  he  is  an  object  of  experimental  interest, 
an  educational  guinea  pig.  This  stimulus  is  more 
likely  to  be  potent,  in  my  opinion,  when  the  student 
is  a  member  of  a  class  which  is  unusual  in  size. 

In  the  more  careful  studies,  results  of  which  have 
been  published,  the  class  numbers  have  ranged  from 
"small"  through  ''medium"  to  "large."  The  "small" 
experimental  classes  apparently  have  about  twenty 
to  twenty-five  members;  this  represents  a  more  usual 
experience  to  the  student,  and  he  is  more  likely  to 
be  conscious  of  class  size  when  he  is  a  member  of  a 
large  class  of  seventy-five  or  more  than  when  he  is  in 
a  small  class  or  a  medium-sized  one  of  thirty-five  to 
forty.  The  sizes  that  are  counted  "large"  or  "small" 
vary  greatly,  sometimes  in  the  same  experimental 
treatment,  so  that  frequently  the  comparisons  are 
between  larger  and  smaller  classes,  both  medium  in 
size,  rather  than  between  real  extremes  in  numbers. 


GROUP   BEHAVIOR  I45 

Frequently,  too,  the  teaching  practice  varies  in 
the  two  classes.  Thus  in  one  experiment  the  smaller 
classes  in  high-school  geometry  contained  about 
twenty-five,  while  the  large  ones  had  about  one 
hundred  members.  In  the  large  classes  a  student 
helper  was  present  for  every  ten  class  members. 
These  helpers  were  superior  students  in  geometry  of 
the  preceding  year.  As  nearly  as  I  can  discover,  there 
were  no  student  helpers  in  the  small  classes.  Under 
the  conditions  it  is  perhaps  not  unexpected  that  a 
better  showing  was  made  by  those  in  the  large  classes. 
With  them,  there  were  present  not  only  more  in- 
structors per  student  but  these  were  people  of  nearly 
their  own  age,  who  could  be  approached  without 
hesitation  not  only  in  class  but  out  of  class  and  even 
out  of  school  hours.  Every  mature  teacher  knows 
that  even  with  the  best  intention  and  the  most  demo- 
cratic attitude,  age  differences  widen  the  gap  between 
the  teacher  and  the  taught,  whatever  other  compen- 
sations there  may  be. 

The  most  comprehensive  experiments  I  have  seen 
reported  in  this  field  are  those  of  the  sub-committee 
on  class  size  of  the  committee  on  educational  re- 
search at  the  University  of  Minnesota.  (66)  These 
were  carried  on  at  the  college  level  and  involved  109 
classes  under  twenty-one  instructors  in  eleven  de- 
partments of  four  colleges  in  the  University  of  Min- 


146  THE  SOCIAL  LIFE  OF  ANIMALS 

nesota.  Forty-two  hundred  and  five  students  were 
observed  in  large  classes,  and  1,854  in  small  ones; 
of  these  1,288  were  paired  as  to  intelligence,  sex 
and  scholarship  before  the  experiment  began.  One  of 
each  pair  was  assigned  to  a  large  and  one  to  a  small 
class  in  the  same  subject  taught  by  the  same  instruc- 
tor. In  this  way  the  obvious  variables  were  controlled 
as  well  as  is  humanly  possible,  unless  we  could  have 
a  large  number  of  identical  twins  with  which  to 
experiment. 

In  78  per  cent  of  the  experiments  a  more  or  less 
decided  advantage  accrued  to  the  paired  students  in 
the  large  classes,  and  at  every  scholarship  level  tested, 
the  paired  students  in  the  large  sections  did  better 
work  than  their  pairs  in  the  smaller  ones;  the  excel- 
lent students  appeared  to  profit  somewhat  more  from 
being  in  large  classes  than  their  less  outstanding 
fellows. 

Of  the  available  data,  a  re-examination  of  the  sum- 
maries indicates  that  there  is  on  the  average  a  dif- 
ference in  the  means  in  the  final  grade  of  4.1  points, 
favoring  the  students  in  the  larger  classes.  There 
is  a  statistical  probability  of  matching  this  by 
random  sampling  of  four  chances  in  ten  million 
(P  =  0.0000004),  and  this  despite  the  fact  that  the 
majority  of  the  class  comparisons  did  not  give  signifi- 
cant differences  when  considered  alone. 


GROUP   BEHAVIOR  I47 

The  numbers  in  the  smaller  classes  usually  ranged 
from  twenty-one  to  thirty,  but  in  some  classes 
dropped  as  low  as  twelve;  in  the  larger  classes  there 
were  usually  thirty -five  to  seventy-nine  students;  in 
the  largest,  one  hundred  and  sixty-nine.  Under  the 
conditions  which  prevailed  in  these  classes  in  psy- 
chology, educational  psychology  and  physics,  the  stu- 
dents in  the  larger  class  sections  made  slightly  but 
significantly  higher  final  grades  than  those  in  smaller 
sections  of  the  same  subject  taught  by  the  same 
instructor. 

So  much  for  objective  experiments.  It  happens 
that  subjective  estimates,  made  both  by  teachers  and 
by  students  at  Minnesota,  favor  the  smaller  rather 
than  the  larger  classes.  It  was  even  true  that  the 
students  were  better  satisfied  with  the  marks  re- 
ceived in  smaller  classes  than  they  were  with  the 
slightly  higher  grades  given  them  in  the  larger  sec- 
tions. 

The  general  attitude  seemed  somewhat  like  that 
toward  a  friend  of  mine  who  teaches  general  mathe- 
matics at  Purdue  University.  He  is  an  experienced 
and  excellent  teacher.  His  program  for  one  semester 
required  that  he  should  meet  a  normal-sized  class 
of  thirty  to  thirty-five  at  eight  o'clock,  and  that  at 
nine  o'clock  he  should  meet  a  class  of  double  the  size 
in  a  larger  room,  to  repeat  the  same  subject  matter. 


148  THE  SOCIAL   LIFE   OF  ANIMALS 

At  the  close  of  the  semester  the  two  sections  were 
asked  to  rank  the  instructor  on  many  different  points. 
Uniformly  the  students  in  the  larger  section  rated 
him  lower  than  those  in  the  smaller  section,  in  such 
matters  as  teaching  skill,  pleasantness  of  voice,  neat- 
ness of  appearance  and  personal  attractiveness! 

I  have  had  a  fairly  extensive  teaching  experience, 
which  has  included  work  in  grade-  and  high-school 
teaching,  as  well  as  over  twenty-five  years  of  teaching 
at  the  college  and  university  level,  during  which  time 
I  have  taught  classes  of  almost  all  sizes,  from  those 
of  over  six  hundred  at  the  University  of  California 
to  the  graduate  classes  of  three  or  four  that  come  my 
way;  and  I  must  confess  to  a  personal  prejudice 
against  these  very  large  classes.  Even  when  using  the 
same  lecture  notes,  I  do  not  give  the  same  lecture  to 
five  hundred  students  that  I  give  to  forty  or  fifty. 
On  the  other  hand,  even  with  graduate  classes  and 
advanced  seminars  I  am  prejudiced  in  favor  of  hav- 
ing enough  students,  which  means  at  least  eight  to 
ten,  to  give  a  certain  esprit  de  corps  to  the  group. 
Such  personal  opinions  have  their  value,  particularly 
when  they  click  with  experimental  results  such  as 
those  outlined  by  Hudelson  from  the  experiments 
at  Minnesota.  It  is  unfortunate  that  those  experi- 
ments did  not  test  either  the  upper  or  the  lower 
limits  of  class  size  which  are  conducive  to  good  class- 


GROUP   BEHAVIOR  I49 

room  performance  on  the  part  of  the  students;  and  I 
know  of  none  that  does  test  these  points  adequately. 

Some  of  the  difficulties  which  are  inherent  in  ex- 
perimentation on  the  effects  of  class  size  on  the  rate 
of  learning  in  man  can  be  obviated  by  the  use  of 
non-human  animals.  This  procedure  does  not  solve 
all  the  requirements  for  elegant  objective  experimen- 
tation, and  has  the  additional  real  difficulty  of  elim- 
inating all  possibility  of  adding  subjective  impres- 
sions to  objective  findings,  a  point  which  makes  one 
of  the  strongest  arguments  for  experimentation  on 
man  when  feasible. 

In  some  respects  the  most  completely  controlled 
experiments  on  the  effect  of  numbers  present  on 
the  rate  of  learning  are  those  that  Miss  Gates  and  I 
performed  some  years  ago,  using  common  cock- 
roaches as  experimental  animals.  (52)  Earlier  work 
by  two  independent  investigators  had  shown  that 
cockroaches  can  be  trained  to  run  a  simple  maze, 
and  can  show  improvement  from  day  to  day.  In  our 
experiments  we  found  that  the  cockroaches  could  be 
trained  to  run  the  maze  we  used  by  fifteen  to  twenty- 
five  successive  trials  on  a  given  day,  and  showed  defi- 
nite improvement  both  in  time  taken  to  run  the 
maze  and  in  number  of  errors.  However,  unlike  the 
experience  of  our  predecessors,  these  University  of 


150  THE  SOCIAL  LIFE   OF  ANIMALS 

Chicago  cockroaches  could  not  carry  over  the  effects 
of  training  from  one  day  to  the  next. 

The  reason  for  this  difference  between  our  cock- 
roaches and  those  around  St.  Louis  and  in  Germany 
is  not  known.  It  may  be  that  at  the  University  of 
Chicago,  despite  our  reputation  for  scholarship,  the 
local  cockroaches  have  a  low  IQ,  or  it  may  be  that 
since  we  used  animals  from  the  bacteriological  lab- 
oratory, because  of  their  unusual  size  and  physical 
vigor,  we  were  unconsciously  selecting  the  dumber 
sort.  Or  perhaps,  contrary  to  our  plan,  we  set  them  a 
problem  which  is  intrinsically  more  difficult  for  the 
cockroach  mentality.  In  any  event,  it  is  important  to 
remember  that  our  cockroaches  forgot  overnight  any- 
thing they  may  have  learned  the  day  before.  As  it 
turns  out,  this  was  fortunate  for  the  experiments  we 
were  carrying  on,  because  we  could  match  up  indi- 
vidual cockroaches  with  the  same  speed  of  learning 
in  pairs  or  groups  of  three  for  later  tests  without  fear 
of  a  carryover  from  their  previous  experience. 

The  maze  used  is  shown  in  Figure  26.  It  consisted 
of  a  metal  platform  from  which  three  runways  ex- 
tended, each  about  two  inches  wide  and  a  foot  or  so 
long.  The  two  side  runways  ended  blindly,  but  the 
center  one  led  to  a  black  bottle,  which  allowed  the 
cockroaches  to  escape  from  the  light.  This  apparently 


GROUP   BEHAVIOR  I5I 

was  a  reward  for  cockroaches  which,  when  possible, 
give  a  negative  reaction  to  light. 

The  three-pronged  set  of  runways  was  mounted 
about  half  an  inch  above  a  pan  of  water,  which  the 
majority  of  the  cockroaches  tended  to  avoid,  and  so 
kept  on  the  runways.  The  tests  were  all  made  in  a 


Fig.  26.     A  simple  maze  used  in  training  cockroaches. 

dark  room  and  light  was  furnished  by  a  single  elec- 
tric bulb  mounted  just  above  the  point  where  the 
central  runway  left  the  main  platform.  In  other 
words,  the  cockroaches,  which  are  negative  to  light, 
had  to  learn  to  run  through  the  area  of  strongest 
illumination  in  order  to  reach  the  dark  bottle  which 
served  as  a  reward.  After  two  minutes'  rest  in  the 
dark  bottle  the  cockroaches  were  literally  poured  out 
onto  the  platform  of  the  maze  without  being  touched 
by  the  experimenter,  and  observation  of  them  began 
again. 

The  problem  as  set  was  about  at  the  limit  of  cock- 


152 


THE  SOCIAL   LIFE  OF  ANIMALS 


roach  ability.  Approximately  one-third  of  the  insects 
tested  never  learned  to  stay  on  the  maze;  whenever 
they  were  placed  on  it  they  proceeded  immediately  to 
run  off  into  the  underlying  water.  Of  the  two-thirds 


n 

16 
15 
14 
13 
12 
U 


9- 

8- 


isoIa."tecL  * 
paired 
J  roup  of  3 


\ 


I 

15 
Trials 


— r- 
20 


25 


Fig.  27.  Isolated  cockroaches  make  fewer  errors  on 
the  maze  than  the  same  animals  paired,  and  still  fewer 
than  if  three  are  being  trained  together. 


GROUP   BEHAVIOR 


153 


that  did  learn  to  remain  on  the  maze,  a  half,  or  an- 
other third  of  all  those  tested,  did  not  show  improve- 
ment in  speed  of  reaching  the  bottle,  after  repeated 


12- 

isola-tecL   •— * 

U- 

paired      

^roup  of  3  •—• 

10- 
9- 

8- 
0    7- 

t  (>■ 

c 
f    5- 

\ 
\ 

A- 

>s^^^ 

3 

^ . 

2- 

1- 

10 


15 
Trials 


20 


25 


Fig.  28.     They  also  take  less  time. 

trials.  Thus  only  one-third  of  the  cockroaches  we 
tested  showed  improvement  with  experience,  and, 
as  I  said  before,  they  forgot  overnight  all  that  they 
learned  during  the  day. 

As  shown  in  the  summarizing  graphs  (Figures  27 
and  28),  isolated  cockroaches  made  fewer  errors  per 
trial   throughout  the  whole   training  period.  They 


154  THE   SOCIAL   LIFE   OF   ANIMALS 

also  took  less  time  to  run  the  maze  than  when  the 
same  animals  were  members  of  pairs  or  of  groups  of 
three.  Turning  the  comparison  around,  paired  cock- 
roaches took  longer  time  per  trial  and  made  more 
errors  than  when  isolated,  and  groups  of  three  took 
still  longer  and  made  more  errors  than  those  in  pairs. 

A  study  of  the  rate  of  improvement  shows  that 
during  the  early  part  of  the  training,  as  is  indicated 
by  the  slant  of  the  graphs,  so  far  as  time  spent  is 
concerned,  paired  cockroaches  improved  more  rap- 
idly than  they  did  if  isolated  or  in  groups  of  three, 
and  those  placed  three  together  on  the  maze  im- 
proved somewhat  more  rapidly  than  they  did  when 
isolated.  Thus,  while  the  presence  of  one  or  two  extra 
cockroaches  slowed  down  the  speed  of  reaction  on  the 
maze  and  increased  the  number  of  errors  made  at  all 
times,  yet  the  rate  of  improvement  in  speed  of  re- 
action was  higher  when  more  than  one  was  present. 
There  was,  however,  no  significant  difference  in  rate 
of  improvement  as  measured  by  number  of  errors. 

Excluding  this  one  aspect  of  rate  of  improvement 
in  time  spent  on  the  maze,  in  all  other  phases  of 
the  experiment  isolated  cockroaches  turned  in  a  bet- 
ter learning  performance  than  they  showed  when 
more  were  present.  Evidently  under  the  conditions 
of  our  experiments  the  tutorial  system  usually  works 
best  with  cockroaches. 


GROUP  BEHAVIOR  155 

Essentially  the  same  sort  of  experiment  was  tried 
with  isolated  and  paired  Australian  parrakeets,  which 
are  commonly  called  love  birds.  (11)  Rather  naively, 
perhaps,  I  thought  that  since  these  birds  so  readily 
pair  off,  perhaps  two  might  learn  to  run  a  simple 
maze  more  rapidly  than  a  single  individual  would. 
This  turned  out  to  be  entirely  a  mistaken  idea.  I 
shall  spare  you  the  details  concerning  this  maze;  it 
was  adequate  in  size,  so  that  two  birds  could  pass 
through  practically  abreast.  Almost  all  the  ninety- 
odd  birds  that  were  tested  learned  easily  to  run  the 
maze  and  normally  reduced  their  time  per  trial  from 
about  two  minutes  to  a  few  seconds,  after  six  or 
seven  days  of  training.  Errors  also  were  reduced,  and 
several  of  the  birds  were  trained  so  that  they  ran 
the  maze  day  after  day  with  no  errors  at  all. 

The  selected  summarizing  graphs  (Figures  29  and 
30)  will  outline  the  results  obtained.  It  made  no  dif- 
ference whether  the  birds  were  caged  in  pairs  or 
separately;  if  placed  alone  in  the  maze  the  perform- 
ance was  similar.  If,  however,  two  birds  were  put 
together  in  the  maze,  the  speed  was  reduced  and 
errors  increased  as  compared  with  the  scores  made 
by  isolated  parrakeets.  It  made  no  difference  whether 
two  males,  two  females  or  a  male  and  a  female  were 
trained  in  the  maze  together;  there  was  always  in- 
terference. The  tendency  was  for  the  more  rapid 


156  THE  SOCIAL   LIFE   OF  ANIMALS 

bird  to  slow  down  rather  than  for  the  slower  bird 
to  speed  up.  The  paired  birds  tended  to  take  the 
same  time  and  to  make  the  same  errors.  Given  suf- 
ficient training,  they  might  make  perfect  scores  so 


Trials 


Fig.  29.  Parrakeets  learn  equally  well  if  trained  when 
isolated,  whether  they  are  caged  singly  or  in  pairs.  A, 
time  per  trial;  B,  errors  per  trial. 


GROUP   BEHAVIOR 


157 


far  as  errors  were  concerned,  but  even  after  long 
training  the  performance  of  pairs  was  always  more 


Fig.  30.  Parrakeets  learn  more  rapidly  if  trained 
alone  than  if  two  are  placed  together  in  the  maze.  A, 
time  per  trial;  B,  errors  per  trial,  (The  upper  curve  is 
unsmoothed;  the  lower  three  have  been  smoothed  mathe- 
matically.) 

erratic  than  that  of  isolated  birds.  When  birds  that 
had  been  trained  to  a  consistent  level  of  excellence 
were  exchanged  so  that  those  formerly  isolated  were 
paired  and  those  formerly  paired  were  isolated,  their 
behavior  in   the  maze   took   on   the   characteristics 


158  THE  SOCIAL  LIFE  OF  ANIMALS 

usually  shown  by  paired  and  by  isolated  birds,  prov- 
ing that  the  type  of  reaction  given  was  a  result  of 
the  numbers  present  rather  than  of  the  working  of 
other  factors.  With  these  love  birds  then,  contrary 
to  the  original  assumption,  all  indications  were  that 
being  paired  in  the  maze  slowed  down  the  rate  of 
learning  and  increased  the  erratic  character  of  their 
behavior. 

Our  experience  with  the  general  problem  did  not 
end  here.  I  teach  at  the  University  of  Chicago  a 
favorite  course  called  Animal  Behavior.  In  this  class 
the  beginning  research  students  attempt  some  small 
problem  and  frequently  make  good  progress  toward 
its  superficial  solution.  One  of  these  student  projects 
has  been  the  training  of  the  common  mud-minnow 
to  react  to  traffic  lights.  The  fish  were  trained  to 
jump  out  of  water  and  obtain  a  bit  of  earthworm 
when  red  was  flashed.  Under  the  green  light  they 
were  conditioned  to  retire  to  one  of  the  bottom  cor- 
ners. If  they  did  jump  under  green  light  they  were 
fed  filter  paper  soaked  in  turpentine.  Within  two 
months  a  lot  of  fishes,  isolated  one  in  each  small 
aquarium,  could  be  trained  so  that  they  would  have 
been  given  an  A  for  the  project  if  they  had  been 
properly  enrolled  students. 

When,  however,  several  fishes  were  placed  together 
in  the  same  aquarium  and  an  attempt  was  made  to 


GROUP   BEHAVIOR  159 

train  all  at  the  same  time  the  rate  of  learning  was 
retarded.  Paired  fish  reacted  as  well  as  if  they  had 
been  isolated,  but  the  reactions  of  groups  of  four 
were  slowed  down,  and  those  of  ten  even  more  so. 
Two  fish  would  rarely  jump  at  once,  and  when  some 
one  individual  was  getting  set  to  jump  for  the  food 
under  the  red  light,  another  would  frequently  come 
along  and  give  him  a  jab  in  the  belly  which  would 
stop  all  tendency  to  jump  for  the  time. 

One  more  instance  remains  to  be  reported.  Dr. 
Welty,  who  has  been  mentioned  before,  undertook 
to  train  goldfish  to  move  forward  from  the  rear 
screened-off  portion  of  an  aquarium  through  a  door 
into  a  small  forward  chamber  where  each  was  fed 
just  after  it  came  through  the  opening.  (118)  An 
aquarium-maze,  similar  to  those  used,  is  shown  in  Fig- 
ure 31.  The  signal  to  the  fish  that  it  was  time  to 
react  came  from  increasing  the  intensity  of  light  in 
the  aquarium  and  opening  the  door  between  the  two 
compartments.  Under  Dr.  Welty's  careful  coaching 
the  fish  improved  rapidly  in  their  speed  of  reaction 
and  usually  had  reached  a  good  level  of  performance 
by  the  sixth  day  of  training. 

In  his  experiments  almost  a  thousand  fishes  were 
trained  at  one  time  or  another.  The  results  of  a 
sample  experiment  are  recorded  in  Figure  32.  In  this 
test  there  were  eight  goldfish,  each  isolated  in  indi- 


i6o 


THE  SOCIAL  LIFE   OF  ANIMALS 


vidual  aquaria,  four  sets  of  paired  goldfish,  two  lots 
of  four  placed  together,  and  one  group  of  eight  in 
one  aquarium.  As  shown  by  the  graph,  there  was  a 


Fig.  31.  Feeding  a  fish  which  has  just  come  through 
the  opening  from  the  larger  side  of  the  aquarium.  (From 
Welty.) 

marked  group  effect  on  the  rate  of  learning.  The 
speed  of  first  performance  of  the  untrained  fishes  was 
most  rapid  with  eight  present  and  slowest  with  iso- 
lated goldfish.  In  the  early  days  of  rapid  learning  the 
same  order  held.  This  experiment  was  repeated  sev- 
eral times  with  identical  results.  Under  these  condi- 
tions there  seems  to  be  little  doubt  but  that  the 


QE37 


100- 


O  ISOLATED 

Q  PAIRS 

•  GROUPS  OF  FOUR 

€  GROUPS  OF  EIGHT 


TRIAL  5  10  14 

Fig.  32.  Goldfish  learn  to  swim  a  simple  aquarium- 
maze  the  more  readily  the  more  fish  there  are  present. 
(From  Welty.) 


i62 


THE  SOCIAL   LIFE   OF  ANIMALS 


groups  of  goldfish  learned  to  move  forward  and  se- 
cure food  more  rapidly  than  the  same  number  of 
isolated  fish. 

The  conditions  of  the  experiments  allow  certain 


TRIAL 


Fig.  33.  Isolated  goldfish  learn  the  problem  set  for 
them  less  rapidly,  and  unlearn  it  more  readily.  (From 
Welty.) 

types  of  analyses  to  be  made.  One  of  these  is  to  test 
the  tenacity  with  which  the  newly  acquired  habit 
will  be  retained.  A  set  of  fish  was  trained  as  usual 
(Figure  33).  After  ten  days,  when  the  grouped  fish 
had  been  letter-perfect  for  four  days,  although  the 
isolated  goldfish  were  still  taking  some  three  min- 
utes per  trial,  the  experiment  was  changed;  when- 


GROUP   BEHAVIOR  163 

ever  the  fish  came  forward  through  the  gate  they 
were  offered  pieces  of  worm  soaked  in  acetic  acid. 
The  isolated  fish,  perhaps  because  they  had  not 
learned  to  perform  so  well,  perhaps  because  they 
were  isolated  or  for  some  other  reason,  ceased  to 
react  rapidly,  and  on  the  twenty-ninth  day  they  were 
averaging  fifteen  minutes  per  trial.  The  grouped 
fish  were  much  more  steady  in  behavior,  and  per- 
sisted in  coming  forward  with  relatively  little  change 
until  the  twenty-seventh  day;  and  even  then  the  old 
conditioning  held  for  most  of  the  fish  most  of  the 
time.  Many  individuals  persisted  in  coming  forward 
through  the  gate  for  a  long  time  after  they  ceased 
biting  or  even  swimming  toward  the  acid-treated 
worm. 

When  a  group  of  fish  are  reacting  together,  if  a 
given  individual  moves  forward  through  the  gate  to 
the  feeding  space,  others  may  follow  because  of  a 
group  cohesion.  It  is  obvious  that  if  a  fish  is  isolated 
and  moves  forward,  the  faster  reaction  cannot  affect 
the  behavior  of  other  isolated  fish. 

With  this  in  mind.  Dr.  Welty  undertook  a  series 
of  experiments  in  which  there  were  two  partitions 
in  the  aquarium,  with  one  door  opening  forward 
and  another  door  opening  through  the  other  parti- 
tion toward  the  rear  of  the  aquarium  (Figure  34). 


164  THE  SOCIAL   LIFE   OF  ANIMALS 

The  fish  were  placed  in  the  central  space  and  those 
in  half  the  tanks  were  trained  to  come  forward  as 
usual.  In  the  other  half,  two  selected  fish  were  con- 
ditioned to  come   forward  and  two  were  similarly 


A ^ 


V 


Fig.  34.  The  aquarium-maze  used  in  training  part  of 
the  fish  to  come  forward  and  part  to  go  to  the  rear  to 
be  fed.  (From  Welty.) 

trained  to  move  to  the  rear  compartment  to  be  fed. 
The  experiment  was  tried  several  times  with  gold- 
fish, the  minnow,  Fundulus,  common  at  Woods  Hole, 
and  another  marine  minnow,  Cyprinodon.  For  one 
reason  or  another,  only  one  series  in  which  the  fish 
were  comparable  was  successfully  completed.  The  re- 
sults are  shown  in  Figure  35.  Generally  speaking, 
the  cohering  groups  of  Cyprinodon  learned  more 
rapidly  and  reacted  more  steadily  than  the  separat- 
ing groups.  This,  then,  is  one  factor  that  is  working, 


GROUP   BEHAVIOR  165 

at  least  at  times,  in  causing  grouped  fish  to  learn 
more  rapidly  in  a  simple  aquarium-maze  than  iso- 
lated fishes  under  similar  treatment. 

As  the  goldfish  move  forward  in  the  usual  divided 

ojo.i' 


e  SEW\RATinG  GROUPS 
O  COHERIMQ  GROUPS 


TR»AL  5  10  J5  19 

Fig.  35.  Cyprinodon  learn  to  move  in  a  body  more 
readily  than  to  split  into  two  separate  groups.  (From 
Welty.) 

aquarium  there  comes  a  time  when  one  or  more  fish 
may  be  in  front  of  the  screen,  and  the  others  in  the 
rear  of  this  advance  guard.  It  was  obviously  a  part 
of  the  investigation  to  find  the  effect  these  more 
rapidly  reacting  fish  had  upon  their  fellows  merely 
as  a  result  of  being  in  the  forward  chamber.  Con- 
ceivably they  may  have  served  as  a  lure.  Another  pos- 


i66 


THE   SOCIAL   LIFE   OF  ANIMALS 


sibility  is  that  a  rapidly  learning  individual  becomes 
a  leader  in  the  reaction  of  the  whole  group. 

Both  of    these    possibilities    were    tested    experi- 


Qli5* 


70 

•  9 

^                 OCOMTROL 

60 

\                ©PLUS  LURE 

\               •  PLUS  LEADER 

50 

•    #1 

40 

■  u 

30 

■   n 

20 

■     \l 

to 

f^io 

D 
C 

-  \_ 

OCOMTROL 
©PLUS  LURE 
•  PLUS  LEADER 


TRIAL 


4     5 

A 


Fig.  36.  Goldfish  learn  more  readily  if  accompanied 
by  a  trained  leader  than  if  there  is  a  fish  in  the  proper 
position  to  act  as  lure.  (From  Welty.) 

mentally  by  Dr.  Welty,  with  results  which  are  sum- 
marized in  Figure  36.  Three  sets  of  aquaria  were 
established.  In  the  control  aquaria  all  the  goldfish, 
of  which  there  were  four  in  each  tank,  were  fish 
which  had  had  no  previous  experience  in  these  ex- 
periments. These  were  trained  as  usual.  In  another 
set,  an  untrained  fish  was  kept  in  each  forward  com- 


GROUP   BEHAVIOR  167 

partment  as  a  lure  and  four  untrained  fish  were 
placed  in  the  rear  compartment.  These  fish  were 
trained  as  usual;  the  so-called  lure-fish  was  fed  after 
the  first  of  the  untrained  lot  came  through  the  gate- 
way. In  the  final  set  of  aquaria  a  trained  fish  was  in- 
troduced along  with  the  four  untrained  fish.  When 
the  light  was  admitted  and  the  gate  was  raised  this 
trained  fish  moved  forward,  came  through  the  gate- 
way, and  was  fed  immediately.  The  others  followed. 
As  the  graphs  show,  after  the  first  day  there  was  lit- 
tle difference  in  the  reactions  given  by  the  control 
fish  and  by  those  which  had  a  lure-fish  in  front  of 
the  screen.  The  fish  with  a  trained  leader  generally 
gave  more  rapid  reactions  than  either  of  the  others. 
There  is  always  a  temptation  to  make  comparisons 
between  the  learning  behavior  of  these  laboratory 
animals  and  that  of  men.  Direct  comparisons  should 
usually  be  avoided.  However,  in  human  terms,  the 
goldfish  reacted  more  rapidly  in  the  presence  of  a 
trained  leader  which  went  through  the  whole  be- 
havior process  with  them,  than  they  did  to  the  pres- 
ence of  one  of  their  kind  as  a  lure-fish  in  the  forward 
compartment,  a  sort  of  signpost  to  proper  behavior. 
Evidently  leaders  working  with  these  goldfish  can  in- 
fluence them  more  than  fish  which  by  their  posi- 
tion merely  show  them  where  they  can  come.  It 
seems  fair  to  say  that  with  these  fish  demonstration 


i68 


THE  SOCIAL   LIFE   OF  ANIMALS 


teaching  is  the  most  effective  method  yet  discovered. 

Still  another  attempt  was  made  to  study  group 

cohesion  in  these  goldfish.  For  this  purpose  aquaria 


Fig.  37.  An  aquarium-maze  arranged  to  test  the 
power  of  observation  of  fish  placed  in  the  side  compart- 
ment. (From  Welty.) 

were  arranged  like  those  in  Figure  37.  At  the  side 
of  the  usual  aquarium-maze  a  narrow  runway  was 
placed  into  which  untrained  goldfish  were  intro- 
duced. In  half  of  the  tanks  the  glass  partition  was 
clear  and  allowed  the  fish  to  see  the  reaction  of  those 


GROUP   BEHAVIOR 


169 


in  the  larger  aquarium-maze.  In  the  other  half,  the 
partition  was  of  opaque  glass,  cutting  off  the  view. 


O  CLEAR  GLASS 
0  OPAQUE  GLASS 


t         2 
TRIAL 

Fig.  38.     Goldfish  react  more  rapidly  if  allowed  to  watch 

others  perform.  (From  Welty.) 

Trained  fish  were  placed  in  the  aquarium-maze 

and  were  run  through  their  performance  from  ten 

to  twenty  times  in  different  experiments.  The  same 


170  THE  SOCIAL   LIFE   OF  ANIMALS 

treatment  was  given  the  fish  in  the  aquaria  with 
opaque  partitions  and  those  with  clear  glass.  The 
trained  fish  were  then  removed  and  those  from  the 
small  side  chamber  were  gently  transferred  to  the 
larger  side.  An  hour  later  they  were  given  an  ordi- 
nary test  such  as  had  been  given  to  the  trained  fish. 
As  is  clearly  shown  by  the  graphs  in  Figure  38,  the 
fish  which  had  been  able  to  watch  the  others  react 
behaved  decidedly  more  like  trained  fish  than  those 
which  had  not  been  able  to  see  their  fellows  perform. 

As  a  final  check,  the  whole  test  was  repeated,  ex- 
cept that  no  fish  were  placed  in  the  larger  side  of 
the  aquarium.  Fifteen  times  each  aquarium  was 
lighted  up,  the  door  opened,  and  the  experimenter 
stood  ready  to  feed  any  imaginary  fish  that  might 
come  through.  Then  when  those  in  the  side  passages 
were  transferred,  there  was  no  essential  difference  in 
the  behavior  of  the  fish  from  the  two  types  of 
aquaria,  and  the  experimenter  was  free  from  any  sug- 
gestion that  he  might  have  been  signaling  the  fish. 

The  results  of  these  experiments  suggest  that  there 
is  such  a  thing  as  imitation  among  goldfish.  Whether 
there  is  or  not  depends,  as  Dr.  Welty  rightly  says, 
largely  upon  the  definition  given  to  the  word  imita- 
tion. These  fish  probably  do  imitate  each  other  on 
a  relatively  simple  instinctive  level.  The  untrained 
fish  that  watched  the  reaction  of  their  trained  fel- 


GROUP  BEHAVIOR  171 

lows  through  the  clear  glass  became  conditioned  in 
two  ways  which  were  not  open  to  the  fish  behind 
an  opaque  glass.  In  the  first  place  they  saw  the  fish 
move  forward  on  the  reception  of  a  given  stimulus, 
pass  through  the  gate,  receive  food,  and  give  no  evi- 
dence of  an  avoiding  or  "fright"  reaction.  This  prob- 
ably gave  what  might  be  called  a  certain  reassurance. 
Secondly,  they  showed  group  cohesion,  and  moved 
forward  with  the  reacting  fishes;  at  times  they  were 
even  seen  to  move  forward  in  advance  of  the  fishes 
on  the  maze  side  of  the  aquarium. 

When  transferred  to  the  aquarium-maze  and  given 
the  releasing  stimulus  of  an  increase  in  light,  accom- 
panied by  the  opening  of  the  gate,  both  types  of 
previous  experience  probably  played  a  role  in  pro- 
ducing a  faster  reaction.  Fish  behind  the  opaque 
glass  could  have  neither  of  these  helpful  experi- 
ences. When  their  narrow  aquarium  was  flooded 
with  light  they  ordinarily  moved  back  to  the  far  end 
and  remained  there.  There  was  nothing  to  train 
them  to  overcome  this  normally  negative  reaction. 
So  reviewed,  it  must  be  said  that  this  behavior  has 
some  points  of  resemblance  to  what  is  called  imita- 
tion in  other  animals. 

There  is  also  an  element  of  imitation  in  the 
greater  food  consumption  of  grouped  fishes.  One  fish 
sees  another  pursue,  attack  and  consume  a  bit  of 


lyS  THE  SOCIAL   LIFE   OF  ANIMALS 

food  and  its  own  feeding  mechanism  is  set  off  as  a 
result  of  this  visual  experience,  even  though  its  own 
hunger  might  not  have  been  sufficient  to  stimulate 
feeding  behavior.  It  is  difficult  to  say  to  what  ex- 
tent such  behavior  is  an  expression  of  competition 
as  contrasted  with  unconscious  co-operation.  The 
two  types  of  motivation  overlap  here  and  elsewhere. 

The  evidence  which  we  have  been  considering 
furthers  our  understanding  of  the  fundamental  na- 
ture of  group  activities  among  many  animals,  some 
of  which  are  not  usually  regarded  as  being  truly  so- 
cial. The  whole  emphasis  of  this  chapter  has  been 
laid  upon  facilitation  as  the  result  of  greater  num- 
bers being  present.  This  kind  of  social  facilitation 
has  been  described  for  such  diverse  processes  as  breed- 
ing behavior,  eating,  working  and  learning. 

Added  numbers  do  not  always  facilitate  these  ac- 
tivities, as  was  shown  by  the  analyses  of  the  effect 
of  numbers  upon  the  rate  of  learning.  With  some 
animals,  for  example  men  and  goldfish,  under  cer- 
tain situations,  learning  is  more  rapid  with  several 
present;  but  with  others,  such  as  parrakeets  and  mud- 
minnows,  under  the  conditions  tested,  increased  num- 
bers lead  to  a  lower  rate  of  learning.  It  seems  that 
no  all-inclusive  positive  statement  can  as  yet  be  made 
in  this  field.  One  can,  however,  make  the  affirmation 
that  in  the  general  realm  here  considered  the  pres- 


GROUP   BEHAVIOR  173 

ence  of  additional  numbers  by  no  means  always  re- 
tards, and  is  frequently  stimulating.  As  before  with 
regard  to  other  processes,  we  find  that  in  certain 
cases  there  are  ill  effects  of  undercrowding  as  well 
as  ill  effects  of  overcrowding.  Without  careful  ex- 
perimental exploration,  we  cannot  predict  which 
effect  will  emerge  from  a  given  situation. 

One  other  result  comes  from  these  studies  which 
will  help  us  to  clarify  evidence  still  to  be  presented, 
as  well  as  to  review  that  already  given.  We  have 
come  upon  another  measure  of  the  existence  of  so- 
cial behavior.  Reactions  may  be  regarded  as  social 
in  nature  to  the  extent  that  they  differ  from  those 
that  would  be  given  if  the  animals  w^ere  alone.  Such 
differences  are  frequently  quantitative,  as  they  have 
been  in  the  cases  we  have  discussed,  although  quali- 
tative differences  occur  as  a  result  of  a  change  in 
the  numbers  present. 

From  this  point  of  view  social  behavior  may  have 
or  may  lack  positive  survival  value.  All  that  is  nec- 
essary is  that  the  behavior  be  different  from  that 
which  would  be  given  if  the  animal  were  solitary. 
In  this  sense  all  the  animals  whose  behavior  we  have 
been  discussing  are  social  to  a  considerable  degree; 
the  more  so,  the  greater  the  difference  between  their 
behavior  when  grouped  and  when  isolated. 

When  the  behavior  of  such  animals  as  cockroaches, 


174  THE  SOCIAL  LIFE  OF  ANIMALS 

fishes,  birds  and  rats  shows  evidence  of  distinct  modi- 
fication as  a  result  of  more  than  one  being  present, 
we  have  another  suggestion  that  there  exists  a 
broad  substratum  of  partially  social  behavior.  There 
are  many  indications  that  this  extends  through  the 
whole  animal  kingdom.  From  such  a  substratum, 
given  suitable  conditions,  societies  emerge  now  and 
again  as  they  have  among  ants  and  men.  At  these 
higher  social  levels,  as  is  to  be  expected,  the  type 
of  behavior  shown  under  many  conditions  is  related 
even  more  closely  to  the  number  of  animals  present 
than  with  less  social  cockroaches  and  fish. 


VI. 


Group  Organization 


WE  ALL  know  that  human  society  is  more  or  less 
closely  organized.  Sometimes,  as  in  military  circles, 
some  business  organizations,  and  certain  universities, 
there  is  a  line  organization  which  extends  in  a  defi- 
nite order,  step  by  step  from  the  highest  official  to 
the  lowest  rank.  Frequently,  however,  the  organiza- 
tion is  more  complex,  intricate  and  temporary. 

We  have  known  for  some  time,  too,  that  in  herds 
of  the  larger  mammals,  where  one  can  distinguish 
different  individuals,  the  group  may  be  organized  to 
some  extent  with  a  dominant  leader  and  frequently 
with  sub-leaders  that  stand  out  above  the  common 
run  of  the  herd.  (16) 

Despite  this  knowledge  we  have  found  with  sur- 
prise that  other  animal  groups,  a  flock  of  birds  for 
example,  in  which  the  different  birds  are  indistin- 
guishable to  the  human  eye,  also  are  organized  into 
a  social  hierarchy,  frequently  with  a  well-recognized 
social  order  which  runs  through  the  entire  flock. 
The  situation  that  has  been  revealed  in  these  flocks 

175 


176  THE   SOCIAL   LIFE   OF   ANIMALS 

of  birds  is  amusing,  interesting  and  important 
enough  to  warrant  more  attention  than  it  is  receiv- 
ing at  present. 

Studies  of  the  sort  I  am  going  to  describe  were 
initiated  by  a  Norwegian  named  Schjelderup- 
Ebbe.  (108)  They  were  made  possible  by  the  use 
of  colored  leg  bands  and  other  markings  by  which 
the  different  individuals  could  be  recognized  by  a 
human  observer.  Apparently  the  birds  themselves 
knew  the  individual  members  of  the  flock  without 
such  artificial  aids. 

Not  because  it  is  the  most  important  work  on  the 
subject,  but  because  I  can  best  vouch  for  it  in  de- 
tail and  in  general,  I  shall  present  certain  analyses 
of  group  organizations  that  have  been  made  in  our 
own  laboratory. 

The  organization  of  flocks  of  chickens  is  fairly 
firmly  fixed.  This  is  particularly  the  case  with  hens. 
The  social  order  is  indicated  by  the  giving  and  re- 
ceiving of  pecks,  or  by  reaction  to  threats  of  peck- 
ing; and  hence  the  social  hierarchy  among  birds  is 
frequently  referred  to  as  the  peck-order. 

When  two  chickens  meet  for  the  first  time  there 
is  either  a  fight  or  one  gives  way  without  fighting. 
If  one  of  the  two  is  immature  while  the  other  is 
fully  developed,  the  older  bird  usually  dominates. 
Thereafter  when  these  two  meet  the  one  which  has 


GROUP    ORGANIZATION  177 

acquired  the  peck-right,  that  is,  the  right  to  peck 
another  without  being  pecked  in  return,  exercises  it 
except  in  the  event  of  a  successful  revolt  which,  with 
chickens,  rarely  occurs. 

The  intensity  of  pair  contact-reactions  varies 
greatly.  A  superior  may  peck  a  subordinate  severely, 
or  lightly,  or  it  may  only  threaten  to  do  so.  It  usually 
turns  its  head,  points  its  bill  toward  the  subordinate 
and  takes  a  few  steps  in  that  direction.  It  may  then 
give  a  low  deep  characteristic  sound  which  fre- 
quently accompanies  an  actual  peck,  and  stretch  its 
neck  up  and  out  without  the  resulting  peck  which 
it  seems  just  ready  to  administer. 

The  peck,  when  actually  delivered,  may  be  light, 
heavy,  or  slashing.  These  vigorous  pecks  may  be 
painful  even  to  man,  as  anyone  can  testify  who  has 
tried  to  take  a  setting  hen  off  her  nest;  and  particu- 
larly painful  if  repeated  in  the  same  spot.  The  peck- 
ing bird  may  draw  blood  from  the  comb  or  may 
pull  feathers  from  the  neck  of  the  pecked  fowl.  The 
peck  is  frequently  aimed  at  the  comb  or  the  top  of 
the  head;  often  it  is  not  received  with  full  force,  for 
the  pecked  bird  dodges.  Less  often  the  peck  is  di- 
rected toward  back  or  shoulders. 

The  severity  of  a  peck  which  lands  as  aimed  is 
illustrated  by  a  recent  observation  in  one  of  our 
small  flocks.  One  bird  received  a  vicious  peck  di- 


178 


THE  SOCIAL  LIFE  OF  ANIMALS 


rectly  on  the  top  of  its  head;  it  walked  backward 
two  or  three  feet,  staggered  and  fell,  arose  and  again 
walked  backward  in  a  blind  course  that  took  it  into 
the  bird  that  had  given  the  original  peck.  By  that 


RW  pecks 

all  12 

A,  BG,  BB,  M,  Y,  YY,  BG^, 

GR, 

R, 

GY,  RY,  RR. 

RR   pecks 

11 

A,  BG,  BB,  M,  Y,  YY,  BG^, 

GR, 

R, 

GY,  RY. 

RY    pecks 

10 

A,  BG,  BB,  M,  Y,  YY,  BG2, 

GR, 

R, 

GY. 

GY    pecks 

9 

A,  BG,  BB,  M,  Y,  YY,  BG^, 

GR, 

R, 

R      pecks 

8 

A,  BG,  BB,  M,  Y,  YY,  BG^, 

GR, 

GR    pecks 

7 

A,  BG,  BB,  M,  Y,  YY,  BG2. 

BG2  pecks 

6 

A,  BG,  BB,  M,  Y,  YY. 

YY    pecks 

4 

A,  BG,  BB,  M. 

M      pecks 

4 

A,  BG,  BB,         Y. 

Y       pecks 

4 

A,  BG,  BB,             YY. 

BB    pecks 

2 

A,  BG. 

BG    pecks 

1 

A. 

A      pecks 

0 

Fig.  39.     Flocks  of  hens  are  organized  into  a  definite 
social  hierarchy. 

time  the  aggressor  had  turned  to  eating  and  paid  no 
attention  to  this  chance  contact. 

As  a  result  of  patient  watching  of  pecks  received 
and  delivered,  it  is  possible  to  find,  with  a  high  de- 
gree of  accuracy,  the  social  status  of  birds  in  a  rela- 
tively small  flock.  (80)  The  organization  of  one  such 
flock  of  brown  leghorn  pullets  is  shown  in  Figure  39. 
This  peck-order  was  determined  after  sixty  days  of 
observation.  As  shown  by  the  chart,  there  was  a 
regular  line  organization  down  to  the  eighth  bird. 


GROUP    ORGANIZATION  179 

Then  a  triangle  was  encountered  in  which  M  pecked 
Y,  Y  pecked  YY  and  YY  pecked  M;  and  each  of  these 
had  the  peck-right  over  the  remaining  members  of 
the  flock. 

Such  irregularities  are  by  no  means  uncommon 
even  in  well-established  flocks.  A  hen  which  is 
otherwise  the  alpha  bird  in  the  pen  may  be  pecked 
with  impunity  by  some  low-ranking  member,  al- 
though the  latter  is  in  turn  pecked  by  many  birds 
over  which  the  alpha  hen  has  a  clearly  established 
social  superiority.  This  inconsistency  may  result 
from  the  low-ranking  bird  having  first  met  the 
alpha  bird  on  one  of  its  off  days,  gained  the  advan- 
tage in  the  first  combat  and  managed  to  keep  it 
thereafter  with  the  aid  of  the  psychological  domi- 
nance thus  established. 

Similar  social  hierarchies  exist  also  among  flocks 
of  male  birds.  One  flock  of  cockerels,  which  we 
studied  for  seventy  days,  demonstrated  the  social 
order  shown  in  Figure  40  in  which  there  are  six 
triangle  situations  that  run  through  all  the  upper 
part  of  the  social  scale,  but  are  especially  evident  in 
the  middle  ranks  where  B  is  involved  in  four  of 
them. 

Cockerels  are  more  pugnacious  than  pullets,  even 
when  they  are  kept,  as  these  were,  on  a  diet  which 
somewhat  restricts  the  tendency  to  fight.  There  were 


l8o  THE   SOCIAL  LIFE   OF  ANIMALS 

more  revolts  and  these  were  more  likely  to  be  suc- 
cessful. For  example,  in  this  flock  of  cockerels,  the 
four  birds  lettered  in  bold-faced  type  in  Figure  40 
showed  reversals,  and  with  some  the  social  rank  had 

BW  pecks  9:  W,  BY,  G,  RY,  B,  BG,  Y,  R,  GY. 

BR  pecks  8:  W,  BY,  G,  RY,        BG,  Y,  R  BW. 

GY  pecks  8:  W,  BY,  G,  RY,  B,  BG,  Y,     *  BR. 

R  pecks  7:  W,  BY,  G,  RY,  B,  BG,  GY. 

Y  pecks  6:  W,  BY,  G,  RY,        BG,         R. 

GB  pecks  5:  W,  BY,  G,  RY,  B. 

B  pecks  4:  W,  G,  RY,  Y. 

RY  pecks  3:  W,  BY,  G. 

G  pecks  2:  W,  BY. 

BY  pecks  2:  W,  B. 

W  pecks  o. 

In  this  order  there  are  six  triangle  situations  as  follows: 

GY  R  R         GB         B  G 

/  \    /\   A  /\  A  /\ 

B^^ BR  Y-e— GY  Y-^ B  Y^h- B  BY^RV  B-^BY 

Fig.  40.     Cockerels  also  have  a  social  organization  which 
is,  however,  somewhat  more  confused  than  with  hens. 


not  been  finally  determined  even  after  seventy  days 
of  observations.  Thus  BY  was  observed  to  peck  G 
on  six  occasions,  while  G  pecked  BY  eight  times. 
Ideally,  in  work  of  this  kind,  the  birds  should  be 
kept  under  observation  throughout  their  waking 
hours  in  order  that  we  may  have  the  full  history  of 
their  behavior.  Such  prolonged  watching  is  imprac- 
ticable, particularly  since  during  much  of  the  day 
there  is  little  pecking.  Actually,  observations  were 


GROUP    ORGANIZATION  l8l 

restricted  to  the  time  near  feeding,  when  the  birds 
were  most  likely  to  fight.  Taken  together  with  the 
greater  number  of  triangles,  the  reversals  indicate  a 
less  stable  social  order  among  these  male  birds  than 
among  their  sisters. 

For  a  time  there  was  no  completely  dominant  bird 
among  the  cockerels.  BW,  which  stood  highest  in 
general,  was  pecked  by  BR,  which  ranked  otherwise 
just  below  him.  One  day  BR  and  Y  started  to  fight, 
as  they  had  done  many  times  before,  with  BR  win- 
ning. This  time  Y  struck  through  to  the  eye,  which 
closed  as  a  result,  and  BR  retreated.  The  injury  was 
such  that  the  tender-hearted  observer  thought  that 
BR  needed  special  treatment,  and  removed  him  to 
a  hospital  pen.  The  eye  healed,  and  two  weeks  later 
the  recovered  bird  was  returned  to  the  flock  which 
he  had  almost  dominated.  In  these  two  weeks  of 
absence  he  had  lost  his  social  status  entirely,  and 
was  pecked  even  by  W,  which  had  not  been  seen 
before  to  peck  a  fellow  cockerel.  The  reason  for  his 
loss  of  position  is  not  clear.  He  had  been  severely 
injured,  he  had  lost  a  fight  to  an  inferior,  and  he 
had  been  absent  from  the  flock  for  fourteen  days. 
For  one  or  all  of  these  reasons  he  had  lost  caste  so 
completely  that  five  days  later  he  had  to  be  removed 
from  the  flock,  literally  to  save  his  life. 

During  the  five  days  that  BR  was  again  with  the 


l82  THE   SOCIAL   LIFE   OF  ANIMALS 

flock,  he  avoided  contacts  with  others  as  much  as 
possible,  and  spent  a  great  deal  of  his  time  crowding 
under  a  low  shelf  on  which  the  water  dish  was  kept. 
In  our  experience,  the  lowest  ranking  chicken  in  a 
flock  tends  to  avoid  social  contacts  as  BR  did  after 
his  fall  from  superior  position.  Frequently  the  low- 
ranking  birds  show  many  objective  signs  of  fear. 
They  spend  time  in  out-of-the-way  places,  feed  after 
others  have  fed,  and  make  their  way  around  cau- 
tiously, apparently  with  an  eye  out  to  avoid  con- 
tacts. The  lowest  ranking  birds  may  appear  lean,  and 
their  plumage  is  somewhat  more  rumpled  because 
they  have  less  time  to  arrange  it.  Dominant  birds, 
on  the  other  hand,  are  characterized  by  a  complete 
absence  of  signs  of  fear  or  of  any  attempt  to  avoid 
birds  of  lower  ranks.  Some  birds,  usually  those  high 
in  the  peck-order  but  not  at  the  top  of  it,  show  few 
avoiding  reactions  to  their  superiors,  and,  when 
pecked,  apparently  take  it  lightly  and  pass  on. 

Chickens  show  some  other  interesting  reactions 
which  are  related  to  their  position  in  the  social 
hierarchy  to  which  they  belong.  Professor  Murchi- 
son,  a  psychologist  at  Clark  University,  has  reported 
studies  on  the  behavior  of  a  flock  of  six  cocks  and 
five  pullets.  (83)  In  one  series  of  experiments  pair 
after  pair  of  the  cocks  were  selected  at  random  and 
placed  at  either  end  of  a  narrow  runway  behind 


GROUP    ORGANIZATION  183 

glass  doors  which  allowed  them  full  sight  of  each 
other.  When  the  glass  doors  were  opened  the  cocks 
ran  toward  each  other.  The  point  of  meeting  was 
proportional  to  the  relative  position  of  the  two  in 
the  social  scale,  for  the  more  dominant  bird  traveled 
farther  than  the  subordinate  one. 

In  another  experiment  two  cocks  were  placed  in 
small  wire  cages  in  which  they  were  plainly  visible, 
and  these  cages  were  set  in  an  enclosure  about  six 
feet  apart.  If  a  third  male  from  the  flock  were  intro- 
duced into  the  pen  the  free  bird  would  go  toward 
the  caged  cock  which  was  relatively  lower  in  the 
social  scale.  In  this  it  behaved  exactly  opposite  to 
the  females  which  were  members  of  the  same  flock 
and  "acquainted"  with  both  roosters.  A  hen  released 
under  similar  conditions  is  said  to  make  her  way 
toward  the  cock  that  has  the  higher  social  position. 

In  our  studies  we  have  usually  found  that  the 
birds  higher  in  the  social  order  had  more  social 
contacts  than  those  that  were  at  the  bottom  of  the 
peck-order.  The  correlation  is  not  always  exact,  but 
to  date  we  have  found  few  exceptions  to  the  rule 
that  the  bird  lowest  in  the  peck-order  has  the  fewest 
contacts.  A  quantitative  difference,  closely  associated 
with  social  rank,  may  be  found  in  the  number  of 
pecks  delivered  when  there  is  no  difference  in  the 
total  contacts  among  the  upper  birds.  In  a  recent 


184  THE  SOCIAL  LIFE  OF  ANIMALS 

Study  (9)  in  which  four  pens  were  under  observation 
with  five  or  six  pullets  in  each,  out  of  4,400  pecks 
the  ranking  birds  gave  1,800,  the  second  in  the  lists 
gave  1,092,  and  so  on  in  regularly  declining  num- 
bers until  those  next  to  the  bottom  gave  136  and 
the  birds  that  were  lowest  in  their  respective  flocks 
gave  none  at  all. 

Murchison  has  reported  a  variation  of  this  general 
rule.  In  studying  the  sexual  behavior  of  his  birds, 
of  the  three  cocks  that  gave  the  mating  reaction  the 
number  of  treadings  stood  in  direct  relation  to  social 
position,  with  the  ranking  cock  treading  pullets 
most  frequently.  Interestingly  enough,  the  top  pullet 
was  also  the  bird  which  mated  most  frequently,  and 
the  number  of  matings  of  the  remaining  females 
was  in  direct  proportion  to  their  social  position. 
This  appears  to  be  a  special  case  of  the  general  rule 
that  birds  high  in  the  peck-order  have  more  social 
contacts  than  those  that  are  low  in  social  rank. 

These  are  some  of  the  known  relationships  exist- 
ing among  birds  that  have  a  relatively  fixed  group 
organization.  Schjelderup-Ebbe,  (109,  110)  who  has 
made  observations  on  over  fifty  species  of  birds,  in- 
cluding, besides  the  common  chicken,  a  sparrow, 
various  ducks,  geese,  pheasants,  cockatoos,  parrots, 
and  the  common  caged  canary,  is  convinced  that  des- 
potism  is   one   of   the   major   biological   principles; 


GROUP    ORGANIZATION  1  85 

that  whenever  two  birds  are  together  invariably  one 
is  despot  and  the  other  subservient  and  both  know 
it.  He  has  said,  "Despotism  is  the  basic  idea  of  the 
world,  indissolubly  bound  up  with  all  life  and  exist- 
ence. On  it  rests  the  meaning  of  the  struggle  for 
existence."  He  applies  this  principle  to  interactions 
of  men  and  of  other  animals  and  even  to  lifeless 
things.  He  says:  "There  is  nothing  that  does  not 
have  a  despot  .  .  .  usually  a  great  number  of  des- 
pots. The  storm  is  despot  over  the  water;  the  light- 
ning over  the  rock;  water  over  the  stone  which  it 
dissolves";  and  he  cites  with  approval  the  old  Ger- 
man proverb  that  God  is  despot  over  the  Devil. 

This  poetry  of  Schjelderup-Ebbe's  is  striking,  but 
does  it  rightly  interpret  the  facts?  We  have  spent  a 
considerable  amount  of  time  at  Chicago,  investi- 
gating the  social  order  of  various  birds.  Messrs. 
Masure,  Shoemaker,  Collias  and  Kellogg  and  Miss 
Bennett  have  been  particularly  active  iii  this  work. 
We  have  not  yet  studied  as  many  varieties  of  birds 
as  Schjelderup-Ebbe,  and  we  have  no  experience  to 
report  about  the  relation  between  God  and  the 
Devil.  Of  the  birds  we  have  studied,  only  the  flocks 
of  white-throated  sparrows  approach  the  common 
chickens  in  the  fixity  of  their  social  hierarchies,  and 
they  do  not  equal  it.  The  common  pigeon,  the  ring 
dove,  the  common  canary  and  parrakeets  show  a  less 


l86  THE   SOCIAL   LIFE  OF  ANIMALS 

rigid  type  of  social  organization  which  I  can  illus- 
trate by  explaining  the  situation  as  we  have  found 
it  among  common  pigeons.  (80) 

The  observations  were  made  on  a  group  of  four- 
teen white  king  pigeons,  half  of  which  were  male 
and  half  female.  Their  social  order  was  observed  in 
sex-segregated  flocks  until,  after  a  month,  it  seemed 
to  be  fairly  stable;  then  the  flocks  were  combined, 
and  after  a  month  during  which  five  of  the  seven 
possible  pairs  mated,  the  sexes  were  again  segregated 
for  twenty-eight  days  of  further  study.  The  results 
are  essentially  similar  both  for  the  males  and  the 
females  for  the  period  when  the  sexes  were  separate, 
so  that  I  shall  follow  only  the  reactions  of  the  fe- 
male flock.  The  essential  facts  can  be  described  with 
the  aid  of  the  diagrams  in  Figure  41.  These  show 
the  social  interactions  between  the  females  lowest  in 
the  social  order. 

Let  us  examine  Chart  A  with  some  care.  This 
charts  the  relationships  of  the  five  birds  that  were 
lowest  in  the  pre-mating  flock.  All  these  were  domi- 
nated in  the  main  by  BY  and  BB.  The  figures  show 
that  BR  was  seen  to  peck  GW  ten  times  and  was 
pecked  by  GW,  and  retreated  from  her  nine  times. 
GW  pecked  BW  thirteen  times,  but  lost  in  four 
encounters.  BR  won  ten  and  lost  seven  of  its  ob- 
served contacts  with  BW,  which  won  thirteen  and 


GROUP    ORGANIZATION 


187 


lost  ten  with  RY.  RY  in  turn  was  practically  even 
(eight  to  seven)  with  BR  and  slightly  ahead  in  its 
relations  with  GW  and  RW.  I  do  not  intend  to  sug- 


GW 


12:27 


mv 


GW 


>BW 


8:14 


RfV 


^BW 


RY<r 


■BIV 


13  UO 

A. 


Fig.  41.  In  flocks  of  pigeons  the  organization  is  one 
of  peck-dominance  rather  than  of  peck-right.  The 
pigeons  highest  in  the  social  order  are  omitted  from 
these  diagrams.  A,  the  pre-mating  flock;  B,  the  entire 
period  of  observation;  C,  the  post-mating  flock. 

gest  that  most  of  these  differences  are  important;  in 
fact  that  is  the  point.  With  flocks  which  are  organ- 
ized as  are  these  pigeons,  it  frequently  becomes  diffi- 
cult to  decide  which  bird  stands  higher  in  the  social 
order. 

It  is  important  to  note  that  in  none  of  these  cases, 


l88  THE  SOCIAL   LIFE   OF  ANIMALS 

in  fact  in  only  one  of  all  the  different  reaction  pairs 
whose  behavior  is  summarized  in  these  charts,  was 
there  an  absolute  dominance  of  one  bird  by  the 
other,  and  then  only  two  contact  reactions  were 
seen.  When  all  contacts  throughout  the  whole  period 
of  observation  are  considered,  there  was  at  least  one 
time  for  each  of  the  contact  pairs  when  the  bird 
which  usually  lost  out  dominated  the  contact  reac- 
tion. 

In  Chart  B,  which  shows  all  the  reactions  during 
pre-  and  post-mating,  and  in  C  which  records  the 
contacts  for  the  post-mating  season  only,  the  four 
birds  represented  by  the  diagrams  were  dominated 
by  three  others,  RY,  BY  and  BB.  It  is  worth  empha- 
sizing that  with  these  birds  an  absolute  despotism 
was  not  established.  Even  RY,  which  more  than  any 
other  bird  dominated  the  post-mating  flock,  lost  con- 
tact reactions  to  each  of  the  others  except  to  RW, 
which  was  lowest  of  all.  While  it  was  winning  329 
reactions  it  lost  58,  and  each  of  the  other  females, 
RW  excepted,  dominated  it  at  least  three  times  in 
the  post-mating  observations. 

The  picture  that  emerges  is  one  of  a  flock  which 
is  organized  into  a  social  hierarchy,  but  one  which 
is  not  so  hard  and  fast  as  that  found  with  chickens. 
In  the  long  run  one  becomes  fairly  sure  which  bird 
in  each  of  the  groups  will  dominate  in  the  larger 


GROUP    ORGANIZATION  189 

number  of  their  contacts,  but  the  result  of  the  next 
meeting  between  two  individuals  is  not  to  be  known 
with  certainty  until  it  has  taken  place.  Within  the 
same  hour  and  even  within  a  few  minutes  reversals 
in  dominance  may  take  place  without  anything  un- 
usual in  the  circumstances. 

Putting  the  matter  somewhat  facetiously,  chickens 
appear  to  have  developed  the  sort  of  "line  organiza- 
tion" characteristic  of  a  military  system  or  a  fascist 
state,  while  these  pigeons,  together  with  the  ring 
doves,  canaries  and  parrakeets,  are  more  democratic. 
The  social  hierarchy  among  chickens  is  based  on 
an  almost  absolute  peck-right  which  smacks  strongly 
of  the  despotism  of  which  Schjelderup-Ebbe  writes, 
while  these  other  birds  have  an  organization  based 
on  peck-dominance  rather  than  on  absolute  peck- 
right. 

With  such  birds  social  position  is  not  fixed  once 
and  for  all.  Consider  the  case  of  RY  among  pigeons. 
When  results  were  first  thrown  together  at  the  end 
of  two  weeks  of  observation,  RY  was  at  the  bottom 
of  the  flock,  a  position  which  it  retained  for  twelve 
more  days.  Then  something  began  to  happen.  What 
it  was,  I  wish  I  knew.  RY  began  to  go  up  in  her 
social  world.  After  six  days  she. ranked  a  shaky  third, 
clearly  dominated  on  the  average  by  BY  and  BB. 

Then  the  pigeons  were  allowed  to  mate.  During 


igO  THE  SOCIAL  LIFE   OF  ANIMALS 

the  mating  period  BY,  which  was  top  bird  in  the 
pre-mating  flock  of  females,  and  RY  did  not  pair  off 
with  any  of  the  males.  Again  I  do  not  know  why. 
After  the  experiment  was  finished  RY  was  carefully 
autopsied  and  we  could  find  no  evidence  of  any- 
thing physically  abnormal.  When  the  sexes  were 
again  segregated  RY  was  the  top-ranking  bird  among 
her  fellow  females,  and  remained  so.  She  was  seen 
to  have  loi  contacts  with  BY,  the  former  alpha  bird, 
and  to  win  83  of  them;  she  had  77  observed  contacts 
with  BB,  which  had  formerly  been  second  from  the 
top,  and  defeated  her  53  times.  In  the  pre-mating 
period  RY  lost  two  combats  for  each  that  she  won; 
in  the  post-mating  flock  she  won  five  contacts  for 
each  that  was  lost. 

This  raises  in  a  rather  dramatic  fashion  questions 
as  to  what  qualities  make  for  a  dominant  bird.  This 
problem  is  not  yet  solved.  With  these  birds,  social 
rank  is  in  part  a  matter  of  seniority.  Mature  chickens 
usually  dominate  immature  ones  and  maintain  their 
dominance  long  after  the  former  youngsters  have 
become  fully  mature  and  possibly  physically  able  to 
displace  the  senior  members.  This  is  good  evidence 
that  memory  of  former  defeats  plays  a  role  in  main- 
taining the  social  order  once  it  is  established.  When 
chickens  strange  to  each  other  are  put  together  for 
the  first  time  dominance  usually  goes  to  the  bird 


GROUP    ORGANIZATION  I91 

with  superior  fighting  or  bluffing  ability.  Maturity, 
strength,  courage,  pugnacity  and  health,  all  seem 
essential  qualities  making  for  dominance  among 
chickens.  Luck  of  combat  also  seems  to  play  a  part 
when  one  considers  the  numerous  triangle  situations 
that  have  been  discovered.  Since  cockerels  have  cer- 
tain of  these  qualities  more  than  pullets,  a  male 
bird,  if  present,  dominates  a  flock  of  hens. 

There  seems  to  be  little  if  any  correlation  between 
greater  weight  and  position  in  the  peck-order.  The 
location  of  the  combat  seems  to  be  important. 
Schjelderup-Ebbe  found  that  chickens  in  their  home 
yard  win  more  combats  than  strangers  to  that  yard; 
and  Mr.  Shoemaker  has  reported  that,  with  canaries, 
each  bird  becomes  dominant  in  the  region  near  its 
nest.  (113)  We  found  some  years  ago  that  with 
pigeons  one  might  be  dominant  on  the  ground 
about  the  feed  pan  and  another  have  first  rank  at 
the  entrance  to  the  roosts.  (80) 

With  chickens,  as  I  have  said,  the  larger,  stronger, 
more  pugnacious  males  usually  dominate  the  fe- 
males. This  is  said  to  be  generally  true  in  species 
in  which  the  male  is  larger  or  more  showy  than  the 
female.  With  the  parrakeets,  (11)  whose  social  order 
in  many  ways  resembles  that  of  pigeons,  the  females 
are  dominant  over  the  males  except  in  the  breeding 
season.  While  breeding  and  nesting  are  in  progress 


192  THE  SOCIAL  LIFE  OF  ANIMALS 

positions  are  reversed,  and  a  previously  hen-pecked 
male  may  drive  his  usually  dominant  mate  back 
onto  the  nest  when  she  attempts  to  leave  it.  The 
sexes  in  these  parrakeets  can  be  told  apart  only  by 
slight  differences  in  color. 

When  hens  are  giving  the  brooding  reaction  or 
are  caring  for  small  chickens,  they  become  less  sub- 
missive to  other  hens.  Some  of  the  other  birds,  whose 
social  ranking  has  been  investigated,  move  up  and 
down  in  the  social  scale  according  to  the  phase  of 
the  breeding  and  nesting  cycle  which  they  are  in  at 
the  time. 

It  has  been  reported  that  with  hens  those  high  in 
the  peck-order  have  a  higher  IQ  than  their  more 
lowly  placed  flock  mates.  (72)  The  IQ  was  measured 
in  this  case  by  placing  grains  of  corn  out  on  the 
floor  with  every  other  grain  securely  fastened  down, 
and  finding  the  speed  and  accuracy  with  which  the 
fowls  would  learn  to  peck  at  the  loose  grains  only. 

We  have  had  as  yet  only  the  most  casual  personal 
contact  with  this  problem  so  far  as  chickens  are  con- 
cerned. With  the  parrakeets,  Masure  and  I  could 
find  no  evidence  of  a  positive  correlation  between 
any  aspect  of  ability  to  learn  a  maze  and  social  rank. 

From  this  summary  it  is  evident  that  in  spite  of 
a  great  deal  of  study  we  do  not  know  all  the  factors 
which  determine  the  position  of  birds  in  their  social 


GROUP    ORGANIZATION  193 

order.  There  is  some  suggestion  from  the  effect  of 
broodiness  in  hens  and  from  observations  on  the 
nesting  cycle  in  canaries  that  there  may  be  elements 
of  control  by  hormones.  This  lead  is  being  investi- 
gated actively  at  present,  but  I  have  no  definite  re- 
sults to  report.  (6) 

Some  of  the  complications  in  determining  the  fac- 
tors that  make  for  dominance  are  shown  by  the  pre- 
liminary summary  which  Mr.  Shoemaker  has  given 
me  of  his  studies  on  the  social  hierarchy  in  canaries. 
The  space  available  for  the  caged  flock  is  a  matter 
of  importance.  When  confined  in  relatively  small 
space,  the  social  order  becomes  more  simple  and 
definite  and  there  is  no  complication  over  the  ques- 
tion of  territorial  rights.  With  more  space,  as  for 
example  in  a  large  flight  cage,  individual  territories 
tend  to  become  established  in  which  the  particular 
bird  is  supreme  even  though  it  ranks  low  in  the 
neutral  ground  around  the  bath  bowls,  the  feeding 
places,  or  regions  where  nesting  material  is  stored. 

When  canaries  are  allowed  to  mate  and  small 
nesting  cages  are  supplied  around  the  walls  of  the 
flight  cage,  each  individual  male  is  master  in  its  own 
nest  cage  and  controls  more  or  less  territory  around 
the  cage  entrance.  Under  these  conditions  even  the 
birds  lowest  in  the  social  order  dominate  in  some 
restricted  space  about  their  nest. 


194  THE  SOCIAL  LIFE  OF  ANIMALS 

In  general  these  canaries  show  more  pecking 
among  the  males  than  among  the  females,  and  dur- 
ing the  nesting  period  the  female  does  little  to  de- 
fend the  nest  territory;  that  is  the  work  of  her  mate. 
In  this  home  territory  the  social  dominance  of  the 
male  over  his  fellow  males  is  not  steady  but  varies 
with  different  phases  of  the  breeding  cycle.  During 
the  processes  of  nest-building,  egg-laying  and  incu- 
bation, the  male  tends  to  become  more  dominant. 
This  is  shown  by  an  increase  in  the  size  of  the  ter- 
ritory about  the  nest  which  he  dominates,  and  by 
the  fact  that  when  on  neutral  territory  he  tends  to 
win  more  of  his  pair  contacts.  During  the  rest  of 
the  cycle  the  male  tends  to  lose  dominance  as  meas- 
ured by  both  these  criteria. 

It  is  worth  noting  that  in  the  course  of  these  pul- 
sations in  dominance  the  male  may  not  actually 
move  up  in  the  social  scale  as  determined  by  the 
number  of  birds  which  he  fully  dominates.  He  may 
win  more  of  his  individual  pair  contacts  without 
actually  oversetting  the  usual  trend.  The  same  bird 
may  show  fluctuations  in  dominance  during  the  day. 
Thus  one  male  regularly  dominated  less  territory  of 
an  evening  than  he  did  in  the  morning.  This  may 
well  be  a  matter  of  stamina. 

In  some  cases  the  relation  between  the  sexes  in 
these  canaries  hinges  on  another  complication.  For 


GROUP    ORGANIZATION  I95 

example,  a  female,  15,  mated  with  a  male,  55,  which 
stood  about  midway  in  the  social  order  among  the 
males:  55  dominated  the  other  females  and  all  the 
other  males  dominated  over  15.  However,  of  thirty- 
three  observed  contacts  between  15  and  55,  the  male 
lost  all  but  one!  The  male  parrakeet  will  drive  back 
on  her  nest  the  female  who  has  left  it,  but  55,  like 
other  male  canaries,  coaxed  his  mate  back  to  her  nest 
with  offers  of  food. 

Until  studies  are  further  advanced,  we  cannot  be 
sure  how  many  of  these  complications  which  Mr. 
Shoemaker  has  recorded  for  the  canaries  are  found 
elsewhere  even  among  birds.  It  seems  reasonable  to 
suppose,  however,  that  the  social  hierarchy  is  rarely 
as  simple  in  its  organization  as  a  mere  listing  of  the 
social  ranking  seems  to  indicate. 

With  all  these  birds,  high  rank  in  the  social  order 
of  the  flock  means  much  greater  freedom  of  action, 
more  ready  access  to  food  and  a  generally  less 
strained  style  of  living.  It  is  hard  to  say  whether  in 
nature  it  means  more  than  this,  although  it  seems 
probable  that  in  times  of  food  shortage,  or  other 
phases  of  environmental  stress,  the  ranking  birds 
who  have  the  first  opportunity  at  food  might  readily 
fare  better  than  those  low  in  t,he  social  scale.  Fortu- 
nately, enough  observations  have  been  made  in  na- 
ture so  we  know  that  with  some  species  the  peck- 


196  THE  SOCIAL  LIFE  OF  ANIMALS 

order,  which  has  been  most  studied  in  restricted 
cages  and  pens,  does  occur  in  the  wild. 

The  alpha  bird  in  a  penned  flock  of  chickens  does 
not  necessarily  lead  in  foraging  expeditions  when 
the  flock  has  more  space.  Fischel,  a  German,  reports 
that  when  hens  of  known  peck-order  are  released 
to  forage  in  an  orchard  the  dominant  and  near- 
dominant  birds  may  or  may  not  be  at  the  apex  of 
the  foraging  flock.  (46)  Usually  the  leadership 
changes  from  time  to  time  and  moreover  the  lead- 
ing bird  seems  always  more  or  less  dependent  upon 
her  followers.  If  she  gets  too  far  out  ahead  the  leader 
turns  back  and  rejoins  the  flock  or  waits  for  them 
to  catch  up.  Similar  hesitation  by  the  leader  when 
it  has  advanced  some  distance  in  front  of  its  fol- 
lowers has  been  observed  among  other  animals,  no- 
tably among  ants  and  men. 

This  problem  of  leadership  among  birds  is  related 
to,  but  not  identical  with,  position  in  the  social 
order.  There  are  many  aspects  of  the  problem  into 
which  we  cannot  go  at  present,  pending  a  closer  and 
more  revealing  study  than  has  appeared  as  yet  of 
the  qualities  that  make  for  leadership. 

With  some  herds  or  hordes  of  mammals  leader- 
ship rests  with  an  old  and  experienced  female.  (16) 
In  such  herds  the  females  and  young  frequently 
make  up  the  more  stable  part  of  the  social  group. 


GROUP    ORGANIZATION  197 

to  which  males  attach  themselves  during  the  mating 
season.  With  other  mammals  the  male  is  the  leader, 
and  sometimes  a  jealous  one,  that  drives  other  males 
out  of  the  herd;  although  in  some  cases  several  males 
are  tolerated.  (3) 

Leadership  does  not  always  go  to  the  faster  or 
stronger  animal;  in  fact,  the  position  of  being  out 
in  front  of  the  flock  may  not  mean  real  leadership. 
An  interesting  example  of  such  pseudo-leadership 
has  been  recorded  for  a  mixed  group  of  shore  birds 
observed  by  Mr.  Nichols  of  the  American  Museum 
of  Natural  History.  (85) 

He  found  a  mixed  flock  of  such  birds  which  was 
composed  of  two  young  dowitchers,  with  a  dozen 
black-bellied  plovers  and  a  single  golden  plover. 
Under  these  conditions  certain  of  the  birds  could 
readily  be  distinguished  from  the  others.  When  the 
flock  was  flushed,  the  flight  of  the  golden  plover  was 
comparatively  rapid  and  it  was  soon  ahead  of  all  of 
the  rest.  The  dowitchers  were  slow  and  tended  to 
fall  behind,  and  when  this  happened  the  black- 
bellied  plover  wheeled.  This  affected  both  the  ap- 
parent leader,  the  golden  plover,  and  the  lagging 
dowitchers.  The  former,  finding  itself  alone  with- 
out followers,  rose  above  the.  flock,  took  the  new 
direction  and  dived  down  with  a  few  swift  wing 
beats,  again  the  apparent  leader  of  them  all.  The 


igS  THE  SOCIAL   LIFE   OF  ANIMALS 

slower  dowitchers  took  the  chord  of  the  arc  made 
by  the  wheeling  flock  and  so  caught  up  with  and 
again  became  an  integral  part  of  the  flying  group. 
Soon  again  the  slow  dowitchers  lagged  and  the  whole 
performance  was  repeated. 

These  observations  do  not  reveal  the  stimulus 
which  releases  the  wheeling  mechanism  of  the  main 
flock.  The  simplest  explanation,  that  the  leader,  find- 
ing himself  out  alone  in  front,  starts  to  turn  and 
so  gives  a  stimulus  to  the  keen-sighted  remainder  so 
that  they  also  shift  direction  almost  instantaneously, 
does  not  hold  in  this  mixed  flock,  for  the  observa- 
tions indicate  clearly  that  the  apparent  leader,  the 
golden  plover,  was  following  along  in  front  of  the 
main  flock  as  much  as  the  slow  dowitchers  were  fol- 
lowing along  behind  it. 

Neither  does  this  simple-leadership  sort  of  ex- 
planation fit  the  facts  as  observed  among  wheeling 
flocks  of  other  shore  birds  or  of  pigeons.  In  such 
flocks  the  stimulus  to  turn  frequently  seems  to 
originate  in  one  of  the  flanks,  and  spreads  from  that 
point  rapidly  through  the  flock.  Here  again  the  ap- 
parent leaders  may  not  be  the  actual  ones.  It  is  pos- 
sible, though  we  are  not  yet  sure  of  it,  that  in  such 
flocks  made  of  birds  which  we  cannot  tell  apart,  the 
faster  individuals  also  may  dive  through  the  flock 


GROUP    ORGANIZATION  I99 

to  the  foremost  position,  taking  their  direction  from 
the  whole  flock. 

However  the  signal  for  turning,  originates,  the 
wheeling  takes  place  so  rapidly  that  mythical  ex- 
planations are  still  being  advanced.  I  have  a  small 
book  written  on  the  subject  by  an  English  author, 
called,  Thought-transference  (or  What)  in  Birds? 
(ill)  The  title  correctly  summarizes  the  contents  of 
the  book. 

I  would  not  have  you  conclude  from  my  repeated 
emphasis  on  the  absence  of  definite  leadership  in 
these  flocks  of  birds,  and  on  the  presence  of  a 
pseudo-leadership  when  the  flock  is  really  determin- 
ing the  direction  that  is  taken  by  the  bird  in  front, 
that  there  is  no  real  leadership  among  other  animals 
and  among  men.  And  I  must  make  it  clear  that  here 
I  am  speaking  of  real  leadership  and  not  of  a  peck- 
order,  which,  as  is  true  with  social  position  in  human 
society,  does  not  imply  leadership  at  all.  Such  a  po- 
sition could  not  be  successfully  maintained  by  a  per- 
son trained  in  science  rather  than  in  dialectics.  But 
apparently,  at  least  among  so-called  lower  animals, 
the  leader  is  frequently  as  dependent  on  his  fol- 
lowers as  they  are  on  him,  and  sometimes  even  more 
so.  A  similar  situation  occurs  in  human  affairs  often 
enough  and  under  such  a  variety  of  situations  that 
the  relationship  deserves  more  careful  consideration 


200  THE  SOCIAL   LIFE   OF   ANIMALS 

than  it  usually  receives  when  problems  of  leadership 
are  discussed. 

While  those  of  us  who  have  been  engaged  in  these 
studies  have  probably  never  been  wholly  unaware 
of  the  possibility  of  amusing  cross-references  to  man, 
I  must  insist  that  our  motivation  has  not  been  that 
of  making  an  oblique  attack  upon  human  social  re- 
lations. Rather,  we  have  found  problems  concerned 
with  the  social  organization  of  birds  and  other  ani- 
mals interesting  and  important  on  their  own  ac- 
count. 

We  have,  of  course,  a  feeling  that  different  ani- 
mals have  much  in  common  in  group  psychology 
and  in  sociology,  as  well  as  in  more  distinctly  physio- 
logical processes.  It  is  the  viewpoint  of  general 
physiology  that  we  cannot  understand  the  working 
and  the  possibilities  of  the  human  nervous  system, 
for  example,  without  study  of  the  functioning  of 
the  nervous  systems  of  many  other  kinds  of  animals. 
Similarly  well-integrated  information  has  been  com- 
piled concerning  general  and  comparative  psychol- 
ogy. From  the  same  point  of  view  some  of  us  have 
been  trying  to  develop  a  general  sociology,  which 
even  in  its  present  imperfect  state  allows  human 
social  reactions  to  be  viewed  in  part  as  the  peculiar 
human  development  of  social  tendencies  which  also 
have    their    peculiar    developments    among    insects. 


GROUP    ORGANIZATION  20I 

birds,  fish,  mice,  and  monkeys;  that  is,  among  social 
animals  generally. 

Keeping  this  point  of  view,  and  with  our  back- 
ground of  studies  of  social  organization,  it  is  worth 
while  to  turn  for  a  short  consideration  of  the  actual 
application  of  similarly  objective  studies  in  certain 
human  groups.  I  pass  over  the  possibilities  of  study- 
ing the  peck-order  in  women's  clubs,  faculty  groups, 
families  or  churches,  to  call  your  attention  to  some 
studies  that  have  recently  been  published  dealing 
with  the  social  interactions  of  the  Dionne  quin- 
tuplets, since  these  will  serve  to  throw  light  on  a 
number  of  interesting  points.  (25) 

In  all  questions  of  dominance  in  the  group  or  of 
other  forms  of  social  inequality,  we  come  immedi- 
ately and  continually  upon  the  question  of  the  ex- 
tent to  which  these  observed  social  differences  are  a 
matter  of  heredity  and  to  what  extent  they  follow 
differences  in  training  or  other  environmental  im- 
pacts. This  is  the  old  nature-nurture  problem,  other 
aspects  of  which  have  been  discussed  for  years. 

Driven  by  many  different  kinds  of  evidence,  biolo- 
gists have  come  to  the  conclusion  that  all  men  are 
not  born  equal.  Applying  this  to  social  affairs  we 
have  the  general  assumption  that  many  of  the  ob- 
served differences  in  social  position  are  a  result  of 
the  inherited  differences  depending  on  the  vagaries 


202  THE   SOCIAL   LIFE   OF  ANIMALS 

of  bi-parental  inheritance  and  more  remotely  on 
mutations  of  one  kind  or  another. 

Fortunately  we  have  in  the  case  of  the  Dionne 
quintuplets  a  natural  experiment  which  deserves 
much  attention.  Detailed  biological  studies  which 
appeared  late  in  1937  confirmed  the  general  assump- 
tion that  these  much-discussed  babies  are  an  iden- 
tical set  of  sisters.  Biologically  this  means  that  all 
of  them  have  come  from  one  ovum  which  was  fer- 
tilized by  one  spermatozoan.  Soon  after  fertilization 
the  early  cleavage  cells  separated  and  produced  five 
embryos,  each  with  identical  heredity.  I  shall  not 
give  the  details  of  the  evidence  on  which  this  con- 
clusion is  based.  In  addition  to  looking  so  much 
alike  that  only  their  regular  attendants  can  tell  them 
apart  with  any  degree  of  sureness,  there  are  simi- 
larities in  finger  and  palm  prints,  in  toe  and  sole 
prints,  and  in  other  anatomic  details  which  point 
conclusively  toward  a  common  identical  heredity. 

A  group  of  investigators  from  the  University  of 
Toronto  have  been  studying  the  social  reactions  of 
the  quintuplets  and  have  reported  observations  from 
the  twelfth  to  the  thirty-sixth  month  of  their  age. 
At  first  the  children  were  placed  together  in  a  play 
pen  by  pairs  to  observe  their  interactions;  from  the 
twenty-second  to  the  thirty-sixth  month  they  were 
observed  as  a  group. 


GROUP    ORGANIZATION  203 

The  available  records  do  not  allow  an  exact  com- 
parison with  the  peck-order  I  have  described  for 
various  birds.  The  observers  were  interested  in  re- 
cording and  analyzing  the  following  bits  of  behavior: 

1.  Total  contact  reactions. 

2.  Reactions  of  one  child  toward  another,  which 
they  call  to  reactions.  A  to  reaction  by  one  child 
will  be  a  jrom  reaction  for  the  child  receiving  the 
attention. 

3.  Whether  the  reactions  are  initiated  or  are  re- 
sponse bits  of  behavior.  An  illustration  will  help  to 
make  this  clear.  If  A  pushes  Y,  it  is  regarded  as  an 
initiated  to  reaction  by  A,  while  Y  is  credited  with 
a  from  reaction.  If  Y  pushes  back,  then  this  is  a  re- 
sponse to  reaction  for  Y  and  a  from  reaction  for  A. 

4.  They  also  record  which  child  watched  which 
one. 

I  shall  not  use  all  these  distinctions  for  my  points 
can  be  made  accurately  with  only  part  of  them. 

As  shown  in  Figure  42,  certain  reactions  are 
summarized  in  the  top  row  for  the  entire  period 
from  the  twenty-second  to  the  thirty-sixth  month, 
and  in  the  lower  row  the  same  reactions  for  the  last 
four  months  of  the  study,  from  the  thirty-second  to 
the  thirty-sixth  month.  The  left-hand  diagrams  give 
the  total  contact  reactions  during  these  respective 
periods.  The  center  diagrams  show  the  total  to  reac- 


204  THE  SOCIAL   LIFE  OF  ANIMALS 

tions  and  those  on  the  right  give  the  initiated  to 
reactions. 

Let  us  examine  the  upper  left  figure.  A  had  a 


AGE:  22-36  MONTHS 

740 

375. 

169 

A 

622 

c 

550 

Y 

421 

Fi 

A 

301 

c 

264 

Y 

2?9 

m 

A 

125 

c 

114 

M 

102 

go 

M 

E 

M 

E 

E 

Y 

2 

3 

1 

5 

4 

2 

3 

1 

5 

4 

2 

3 

5 

4 

, 

<— MENTAL  RAWK 

100  84  74  58  54 
TOTAL  CONTACTS 
346 

515 

a' 


132 


2      3      15      4 


100   50    70    61    53 
TOTAL  TO   CONTACTS 
176 

149 


74    68    60    53   «— PER  CENT 


A 

53 

49 

c 

M 

29 

L27 

Y 

E 

?. 

3 

5 

1 

4 

♦—MENTAL  RANK 


100   90    62    52    40 


100    85    61     56    37 
AGE:   32-36  M0NTH5 


67    62    37    34  <— P£R  CENT 


Fig.  42.     The  Dionne  quintuplets  also  show  evidence  of 
a  social  organization  among  themselves. 

total  of  740  observed  contacts  directed  to  and  re- 
ceived from  her  sisters.  This  is  taken  as  lOO  per  cent. 
C  had  similarly  622  contacts,  which  were  84  per 
cent  of  A's,  and  so  on,  with  Y  third,  M  fourth,  and 
E  fifth.  The  order  in  total  number  of  contacts  then 


GROUP    ORGANIZATION  205 

is  A,  C,  Y,  M,  E.  This  same  order  holds  for  total  to 
contacts  and  for  both  total  and  to  contacts  in  the 
thirty-two  to  thirty-six  months'  period.  The  diagrams 
on  the  right  show  that  A  initiated  the  most  to  con- 
tacts, and  that  C  was  next.  Beyond  that  the  order 
varies.  For  the  whole  period  of  observation  (upper 
row)  it  is  M,  E,  Y,  and  for  the  last  period  (lower 
row)  it  stands  as  M,  Y,  E. 

The  other  available  data  do  not  always  give  this 
same  order,  but  enough  has  been  presented  to  show 
that,  among  these  children  identical  in  heredity  and 
almost  so  in  post-natal  environment,  there  are  social 
differences  which  can  be  recognized  by  the  behavior 
of  the  children  toward  each  other. 

As  the  figures  giving  mental  rank  indicate,  the 
correlation  with  intelligence  is  by  no  means  perfect. 
Neither  is  the  correlation  with  size.  Y,  the  largest, 
and  said  in  some  ways  to  be  the  most  mature  of  the 
five,  ranks  in  the  tests  shown  here  from  third  to 
fifth.  And  while  M,  the  smallest,  ranks  low,  she  is 
not  the  lowest,  and  other  data  show  that  in  the  per- 
centage of  her  contacts  which  were  self-initiated  to 
reactions  she  ranks  first  of  all  these  sisters. 

These  observed  differences  raise  an  interesting 
question:  If  heredity  has  been  the  same  and  the 
environment  constant,  how  did  the  differences  creep 
in?  It  is  possible  that  there  are  unobserved,  unrec- 


206  THE  SOCIAL   LIFE  OF  ANIMALS 

ognized  differences  either  in  the  handling  of  the 
children,  in  their  early  contacts  with  each  other,  or 
in  their  impacts  with  their  physical  environment 
which  may  have  been  cumulative  enough  to  pro- 
duce these  social  differences.  It  is  also  possible,  as 
Professor  H.  H.  Newman  suggests,  that  the  differ- 
ences are  environmental  after  all.  We  must  remem- 
ber that  from  the  standpoint  of  A,  C,  Y,  M,  and  E, 
their  environmental  relations  began  long  before 
birth,  and  though  the  care  given  them  since  birth 
may  have  been  practically  identical  in  each  case,  it 
may  not  have  been  possible  to  erase  environmental 
conditions  impressed  upon  them  during  their  seven 
critical  months  of  intra-uterine  life. 

Whatever  the  reason,  we  have  come  to  an  inter- 
esting, and,  I  think,  important  conclusion,  which  is 
that  animals  with  exactly  the  same  heredity  may 
still  develop,  even  at  an  early  age,  graded  social  dif- 
ferences showing  that  one  is  not  exactly  equal  to 
the  other.  We  have  indications  that  the  same  prin- 
ciple holds  among  birds,  but  even  if  present  indica- 
tions are  finally  borne  out,  the  experiment  will  not 
be  as  elegant,  in  the  strictly  scientific  sense,  as  are 
these  observations  on  the  Dionne  quintuplets. 

Finally,  by  way  of  review,  there  exists  among 
flocks  of  birds,  even  though  they  may  be  identical 
to  the  human  eye,  a  graded  series  of  reactions  within 


GROUP    ORGANIZATION  207 

the  flock  which  allow  observers  to  rank  the  birds  in 
the  order  of  their  social  dominance.  This  social 
order  may  be  relatively  hard  and  fast,  as  with  hens, 
or  more  loosely  organized  on  a  give-and-take  basis 
among  pigeons  and  canaries.  The  factors  under- 
lying the  social  order  in  these  birds  are  complicated 
and  include  such  personal  traits  as  age,  pugnacity, 
sex  in  general  and  the  reproductive  cycle  in  par- 
ticular, as  well  as  such  environmental  factors  as  size 
of  available  space  and  the  possibilities  of  establish- 
ing special  territories.  High  position  in  the  social 
order  does  not  necessarily  coincide  with  group  lead- 
ership, although  at  times  it  does.  The  survival  value 
of  high  position  in  the  social  hierarchy  has  not  been 
demonstrated,  but  there  are  many  reasons  for  sus- 
pecting that  it  may  be  felt  in  times  of  famine  or 
during  other  periods  of  environmental  stress. 

The  problems  related  to  leadership,  although 
mentioned,  were  not  discussed  exhaustively.  Em- 
phasis was  laid  on  the  importance  to  the  leader  of 
his  followers,  and  on  the  existence  of  a  pseudo- 
leadership  in  which  the  animal  in  front  is  taking 
direction  from  his  apparent  followers. 

With  the  Dionne  quintuplets  it  was  demonstrated 
that  social  differences  exist  even  with  children  that 
have  identical  heredity,  and  a  theory  of  environ- 
mental differences  was  favored  as  an  explanation. 


2o8  THE  SOCIAL   LIFE  OF  ANIMALS 

In  conclusion,  the  social  organization  observed  in 
birds  and  other  animals  reminds  one  almost  con- 
stantly of  certain  types  of  human  social  situations. 
The  dominance-subordination  relations  of  people 
are  at  times  readily  observed;  at  other  times  they 
are  obscured  by  other  social  responses.  When  present 
in  man,  patterns  of  domination  may  be  expressed  in 
many  more  ways  than  in  birds  or  mice.  It  may  well 
be  that  the  social  hierarchies  of  chickens,  canaries 
and  men  have  much  in  common.  Without  taking 
the  comparison  too  seriously,  the  fact  that  chickens, 
for  example,  have  a  relatively  simple  system  of  des- 
potism may  help  explain,  though  it  does  not  justify, 
the  appearance  of  a  similar  social  organization  in 
man.  Other  types  of  social  organization  also  exist 
among  the  other  animals,  and  man  need  develop 
only  that  best  suited  to  his  unique  situation. 


VII 


Some  Human  Implications 


WHILE  WE  have  been  engaged  in  trying  to  assay 
the  relative  importance  of  the  principle  of  co-opera- 
tion among  animals,  we  have  given  most  of  our  time 
and  attention  to  its  manifestation  among  animals 
considered  to  be  asocial  or  only  partially  social.  In 
such  animals  it  is  an  unconscious  kind  of  mutualism, 
but  its  roots  are  deep  and  well  established  and  its 
expression  grows  to  be  so  spontaneous  and  normal 
that  we  are  likely  to  overlook  or  forget  it  in  the  more 
striking  exhibition  of  social  co-operation  among 
higher  animals.  Conscious  co-operation  is  so  com- 
paratively new  in  an  animal  world  many  millions 
of  years  old,  that  we  may  underrate  its  strength  and 
importance  if  we  are  not  reminded  of  its  foundations 
in  simple  physiology  and  primitive  instinct. 

When  we  attempt  to  apply  to  human  behavior  the 
same  methods  of  analysis  that  we  have  used  through- 
out toward  other  animal  groups,  we  reach  most  in- 
teresting results  when  we  select  some  phase  of  reac- 
tions of  men  in  which  integration  has  not  developed 

209 


210  THE  SOCIAL  LIFE  OF  ANIMALS 

much  beyond  that  found  in  some  of  the  semi-  or 
quasi-social  animal  aggregations  which  we  have  been 
considering  in  the  lower  animals. 

Among  the  possible  aspects  of  human  behavior 
that  meet  this  requirement  and  that  lend  themselves 
to  biological  analyses  is  the  whole  set  of  activities 
that  center  about  the  relations  between  nations. 
Even  the  most  optimistic  humanist  will  not  main- 
tain that  these  are  at  present,  or  ever  have  been,  on 
as  high  a  social  plane  as  that  which  characterizes 
many  of  the  personal  interactions  of  mankind,  or 
those  of  the  smaller  social  groupings  of  men. 

The  most  casual  reading  of  recent  events  is  con- 
vincing evidence  that  the  modern  international  sys- 
tem is  based  on  war.  This  final  resort  to  violence 
has  been  regarded  by  many  thoughtful  people  as  in- 
evitable, man  being  what  he  is,  that  is,  the  product 
by  natural  selection  of  the  results  produced  by  the 
struggle  for  existence;  for  the  ordinary  thoughtful 
person  is  not  aware  that  the  tendency  toward  a  strug- 
gle for  existence  is  balanced  and  opposed  by  the 
strong  influence  of  the  co-operative  urge.  Because 
of  this  common  attitude  toward  war,  and  because 
of  its  fundamental  importance  to  our  species,  I  pro- 
pose to  cut  through  the  shifting  tangle  of  interna- 
tional policies  down  to  the  basic  biological  signifi- 
cance which  it  holds  for  us. 


HUMAN    IMPLICATIONS  211 

In  doing  so  I  must  recognize  these  two  funda- 
mental principles,  the  struggle  for  existence  and  the 
necessity  for  co-operation,  both  of  which,  consciously 
or  unconsciously,  penetrate  all  nature;  and  I  shall 
say  now  that  we  may  find  that  these  two  principles 
are  not  always  in  direct  opposition  to  each  other; 
that  there  is  evidence  that  these  basic  forces  have 
acted  together  to  shape  the  course  of  evolution,  even 
the  evolution  of  social  relations  among  men  and  na- 
tions of  men. 

If,  in  the  past,  we  have  not  had  facts  on  which 
to  base  rational  conclusions  about  national  problems, 
it  cannot  be  said  that  we  have  not  had  powerful 
emotions  to  drive  us  into  one  attitude  or  the  other. 
It  is  very  difficult  to  keep  an  objective,  unemotional 
attitude  toward  the  complex  subject  of  the  biology 
of  war.  We  may  not  agree  in  our  placing  of  the 
emphasis,  but  I  trust  that  when  we  disagree  it  will 
be  on  a  healthy  intellectual  level. 

It  is  clear  that  we  are  entering  a  tricky  field  where, 
to  a  greater  extent  than  usual,  the  evidence  is  not 
all  in,  and  one  in  which  much  that  we  think  we 
know  is  contradictory.  No  one  can  bring  this  prob- 
lem into  the  laboratory  for  careful  testing.  We  must 
do  the  best  we  can  with  inforraation  which  is  more 
incomplete  and  faulty  than  that  on  which  we  nor- 
mally base  our  biological  discussions.  The  human 


212  THE  SOCIAL  LIFE  OF  ANIMALS 

importance  of  the  subject  justifies  the  risk.  The  pres- 
ent discussion  will  center  about  three  main  points: 

1.  To  what  extent  do  the  underlying  biological 
relationships  tend  to  bring  about  war? 

2.  Is  war  biologically  justified  by  the  results  pro- 
duced? 

3.  Can  the  basic  principles  of  struggle  and  of  co- 
operation work  together  in  the  international  rela- 
tions of  men? 

Many  men  are  aggressive  animals.  The  similari- 
ties between  human  social  hierarchies  and  those  of 
chickens  and  other  animals  emphasize  similarities  of 
the  drive  toward  dominance  in  the  species  concerned. 
Our  immediate  question  is:  Does  this  human  aggres- 
siveness mean  that  men  have  an  inherent,  instinctive 
drive  toward  war?  The  ideal  way  to  attack  this  prob- 
lem would  be  to  rear  sizable  groups  of  people  free 
from  contact  with  outside  influence  or  social  tradi- 
tion and  see  whether  under  these  conditions  they 
would  instinctively  engage  in  group  combats  in  order 
to  forward  or  defend  group  ambitions. 

Such  objective  procedure  is  out  of  the  question, 
but  an  interesting  subjective  inquiry  has  been  made. 
In  1935,  American  psychologists  took  a  poll  among 
themselves  on  the  question  as  to  whether  they  be- 
lieved that  the  tendency  toward  making  war  is  an 
instinctive  drive  in  man.  Of  those  answering^,  well 


HUMAN    IMPLICATIONS  213 

over  90  per  cent  said  that  there  is  no  proof  that  war 
is  an  innate  behavior  pattern.  (129)  Less  than  10  per 
cent  thought  that  war  represents  an  instinctive  re- 
action. I  did  not  personally  see  this  questionnaire 
but  I  am  credibly  informed  that  the  question  was 
stated  fairly  and  did  not  suggest  the  type  of  answer 
expected. 

This  is  a  rather  unexpected  unanimity,  and  may 
be  accounted  for  to  a  minor  degree  by  the  existence 
of  one  modern  school  of  psychologists  that  doubt 
the  possibility  of  instinctive  action,  particularly 
among  men.  I  do  not  think  they  represent  a  large 
proportion  of  American  psychologists  but  there  may 
have  been  enough  of  them  to  have  lifted  the  per- 
centage high. 

The  opinion  of  the  psychologists  is  supported  by 
the  independent  judgment  of  one  of  the  leading 
students  of  anthropology,  Professor  Malinow^ski,  who 
said  in  his  Harvard  tercentennial  lecture:  (78)  "All 
the  wrangles  as  to  the  innate  pacifism  or  aggressive- 
ness of  primitive  man  are  based  on  the  use  of  words 
without  definition.  To  label  all  brawling,  squab- 
bling, dealing  of  black  eye  or  broken  jaw,  war^  as  is 
frequently  done,  simply  leads  to  confusion.  War  can 
be  defined  as  the  use  of  organized  force  between 
two  politically  independent  units,  in  the  pursuit  of 


214  THE  SOCIAL  LIFE  OF  ANIMALS 

tribal  policy.  War  in  this  sense  enters  fairly  late 
into  the  development  of  human  societies." 

It  is  not  impossible  to  break  down  and  re-make  in- 
stinctive behavior,  as  the  change  in  marriage  cus- 
toms since  the  days  of  the  cave  man  shows  us.  Never- 
theless, it  is  much  easier  to  change  learned  behavior 
patterns,  one  of  which  these  experts  believe  war  to 
be. 

We  must  still  take  account  of  individual  aggres- 
siveness, and  the  fact  that  man  appears  to  be  rela- 
tively easy  to  lead  into  mass  combat.  Even  if  war- 
making  is  not  instinctive,  if  it  is  a  learned  pattern 
of  social  behavior,  there  is  evidence  that  it  has 
existed  for  some  fifty  centuries,  and  it  would  prob- 
ably require  at  least  a  few  centuries  of  intelligent 
and  fairly  concerted  effort  by  those  who  do  not  be- 
lieve in  its  utility  to  unlearn  the  habit. 

There  is  a  second  important  set  of  biological  proc- 
esses which  at  first  sight  appear  to  work  inevitably 
toward  the  production  of  war.  These  center  about 
the  question  of  overpopulation,  that  is  to  say,  about 
the  relation  human  numbers  bear  to  habitable  land 
areas.  This  is  the  next  primary  problem  which  we 
must  consider. 

Over  the  world  there  is  a  limited  range  of  habit- 
able land;  and  thus  far  we  have  no  intimation  of 
any  practical  method  of  emigration  to  neighboring 


HUMAN    IMPLICATIONS  8I5 

and  perhaps  less  occupied  planets.  And  there  is  a 
rapidly  expanding  human  population,  which  is  even 
now  becoming  uncomfortably  dense  in  the  crowded 
nations.  It  is  often  said  that  this  is  a  fundamental 
cause  of  tension  which  makes  wars  inevitable,  as 
hard-pressed  dense  populations  seek  food  in  more 
amply-provided  areas. 

The  desirable  biological  results  of  wars  so  induced 
have  been,  and  still  are,  supposed  to  be  two: 

1.  The  dense  populations  are  thinned  to  the  bear- 
able point  as  a  result  of  the  fighting,  or 

2.  Superior  nations,  or  races,  are  victors.  They 
expand  at  the  expense  of  the  defeated  inferior  group 
and  so  occupy  more  of  the  limited  space  which  is 
available  for  men. 

Let  us  test  these  theories  against  the  known  facts. 
Roughly  speaking,  there  are  about  fifty-two  million 
square  miles  of  land  surface  on  the  earth.  (95)  This 
includes  the  habitable  plains  of  the  temperate  re- 
gions; it  also  includes  the  relatively  uninhabited 
deserts,  tropical  jungles,  and  mountains.  Approxi- 
mately one-fourth  of  these  fifty-two  million  square 
miles  is  desert  or  semi-desert  and  can  support  only 
a  sparse  population  of  men.  This  leaves  roughly 
forty  million  square  miles  of  non-arid  land  theoreti- 
cally open  to  human  habitation. 

On  this  land  there  are  living  at  present,  accord- 


210  THE  SOCIAL   LIFE   OF  ANIMALS 

ing  to  a  1935  revision  of  the  estimated  world  popula- 
tion which  was  made  by  Professor  Pearl,  something 
over  two  thousand  millions  of  people.  This  is  almost 
exactly  forty  people  per  square  mile  of  the  whole 
earth's  surface,  or  about  fifty  people  per  square  mile, 
if  the  arid  and  semi-arid  land  is  excluded.  We  can 
better  visualize  the  meaning  of  these  figures  when 
we  know  that  they  are  almost  exactly  the  average 
population  density  for  the  United  States;  forty  per 
square  mile  for  the  whole  land  area,  and  fifty  per 
square  mile  if  on  land  with  fair  rainfall. 

A  recent  estimate  of  human  population  of  three 
hundred  years  ago,  tentatively  advanced  by  Profes- 
sor Pearl,  is  that  in  1630  there  were  probably  about 
445  million  people  on  the  whole  earth,  or  about 
eight  per  square  mile  of  total  land  surface.  (95)  Dr. 
Pearl  thinks  that  this  was  probably  the  largest  hu- 
man population  which  the  earth  had  supported  up 
to  that  time.  Then  came  the  opening  of  the  Americas 
for  settlement,  and  the  beginnings  of  modern  use 
of  transport  and  manufacturing  processes,  and  the 
scattering  of  information  by  modern  methods.  The 
result  has  been  that  in  the  last  three  centuries  the 
population  of  the  world  has  increased  almost  five- 
fold, from  eight  to  forty  per  square  mile,  largely 
because  food  and  shelter  and  mechanical  energy  were 
made  available  for  five  times  as  many  people,  and 


HUMAN    IMPLICATIONS  217 

because  the  development  of  modern  science  made 
the  world  safer  for  them. 

In  these  three  hundred  years  the  world  popula- 
tion has  doubled,  on  the  average,  approximately 
every  sixty-four  years.  Today  mankind  is  increasing 
in  numbers  at  such  a  rate  that  if  the  increase  should 
continue  as  it  was  going  in  1935  we  could  expect 
another  doubling  of  the  number  of  people  in  the 
world  in  approximately  seventy  years,  and  we  should 
have  about  eighty  people  per  square  mile  in  the 
year  2005. 

What  then?  Will  not  the  coming  generations  at 
some  time  be  obliged  to  fight  for  their  place  in  the 
sun? 

This  prospect  is  somewhat  altered,  however,  by 
the  fact  that  many  students  of  population  trends 
believe  that  the  rate  of  human  increase  is  slowing 
down.  In  the  case  of  the  United  States,  Dr.  Baker, 
(20)  economist  of  our  Department  of  Agriculture, 
has  estimated  recently  that  unless  present  trends  are 
changed  (and  they  may  be)  there  will  be  a  further 
population  increase  in  the  United  States  of  only 
about  eight  million  in  the  next  two  decades.  He 
thinks  that  the  population  will  then  have  reached 
its  maximum,  if  conditions  remain  as  they  are  today. 
Thus,  according  to  Dr.  Baker,  we  are  looking  for- 
ward to  a  maximum   population   of  less   than    150 


2l8  THE  SOCIAL  LIFE  OF  ANIMALS 

million  people,  or  less  than  fifty  for  every  square 
mile  of  our  country.  Others  put  the  figure  higher, 
but  I  know  of  no  expert  who  expects  our  Ameri- 
can population  to  double  itself  again  unless  there  is 
a  radical  increase  in  available  energy  or  in  other 
aspects  of  our  living  conditions. 

For  the  world  as  a  whole.  Dr.  Pearl  estimated  in 
1936  that,  if  present  trends  continue,  as  they  may 
not,  the  world  population  will  reach  a  maximum  of 
about  2,650  millions  by  the  year  2100.  (95)  This  is 
a  density  of  about  fifty  persons  per  square  mile  of 
land  surface  on  the  globe,  counting  good  and  bad 
land  alike. 

I  must  dissociate  myself  from  any  responsibility 
for  these  and  similar  estimates.  I  fully  realize,  as  do 
their  authors,  the  pitfalls  inherent  in  such  predic- 
tions. Human  trends  being  what  they  are  and  have 
been  in  the  last  three  hundred  years,  this  is  as  good 
an  approximation  as  can  be  made  at  present,  and 
with  all  its  faults  it  is  worth  considering. 

The  important  aspect  to  me  is  that  we  do  not 
have  reason  to  expect  in  the  United  States  or  in  the 
world  a  continuation  of  the  unprecedented  rate  of 
increase  of  the  last  three  centuries,  or  even  a  con- 
tinuation of  the  present  rate  of  increase.  Unless 
population  experts  are  all  at  fault,  the  rate  of  re- 


HUMAN    IMPLICATIONS  219 

production  among  human  animals  is  slowing  down, 
just  as  the  rate  of  increase  in  non-human  popula- 
tions slows  down  as  laboratory  containers  approach 
an  overcrowded  condition.  In  fact,  few  animal  popu- 
lations approach  the  limits  of  their  food  supply  in 
nature. 

The  reasons  for  this  are  not  clear,  though  they 
appear  to  be  connected  with  the  ease  of  securing 
available  energy,  food  and  shelter.  As  men  approach 
the  bearable  limits  of  these  necessities  of  life  there 
occurs  an  increase  in  birth  control.  This  is  shown 
in  Italy,  where,  according  to  figures  given  in  The 
Statesman's  Year  Book,  (114)  despite  continued 
propaganda  for  a  higher  birth  rate  the  actual  num- 
ber of  births  fell  over  12  per  cent  from  1922  to 
1936  (Figure  43).  Thanks  to  a  similar  decline  in 
death  rate  the  significant  percentage  of  births  which 
are  canceled  by  deaths  has  remained  fairly  steady. 
In  England,  where  there  has  been  no  great  effort  to 
encourage  population  increase,  the  deaths  in  1922 
were  62  per  cent  of  the  births;  in  1935  they  were 
81  per  cent.  Perhaps  the  success  of  Italian  efforts  is 
to  be  measured  by  this  comparison  with  England 
rather  than  by  the  fact  that  under  propagandist  pres- 
sure their  birth  rate  has  actually  decreased.  In  Ger- 
many, the  present  regime  has  not  been  in  power 
long  enough  to  establish  a  trend.  The  graph  (Fig- 


220 


THE   SOCIAL  LIFE   OF  ANIMALS 


ure  43)  shows  that  beginning  in  1934  there  has  been 
a  dramatic  decrease  in  the  percentage  of  births  can- 
celed by  deaths;  actually  there  has  been  a  decided 
increase  in  births.  Recent  analyses  in  the  American 


1928       1929       1930      1931        1932       1933.     1934      1935 


Fig.  43.  The  percentage  of  births  that  were  canceled 
by  deaths  for  the  given  years  in  Italy  and  Germany.  The 
higher  the  trend  line,  the  slower  the  population  is  grow- 
ing and  vice  versa.  The  broken  line  connects  the  ob- 
served points;  the  solid  line  shows  the  mathematically 
smoothed  trend  line.  (Data  from  The  Statesman's  Year 
Book.) 


HUMAN    IMPLICATIONS  221 

Journal  of  Sociology  indicate  that  the  present  opin- 
ion is  that  the  increase  in  the  birth  rate  may  be 
the  result  of  a  campaign  against  abortion  which  in 
pre-Nazi  times  terminated  over  one-third  of  the 
pregnancies.  (58,  125)  One  can  deduce  from  general 
biological  experience,  despite  the  current  German 
data,  that  the  population  almost  automatically  ad- 
justs numbers  within  its  physical  and  biological 
limitations.  Doubtless  eventually  this  mysterious 
process  of  population  adjustment  will  be  analyzed. 
At  present  we  have  made  some  progress  toward  an 
understanding  of  the  factors  involved  in  non-human 
populations,  but  have  little  objective  knowledge  to 
report  where  men  are  concerned. 

It  is  of  course  possible  to  increase  the  present 
food  supply  of  the  world  enormously.  It  has  been 
estimated  that  if  our  present  biological  knowledge 
were  consistently  applied  we  could  raise  food  enough 
to  supply  at  least  ten  times  the  present  world  popu- 
lation, instead  of  the  25  per  cent  increase  to  which 
we  are  looking  forward  by  the  year  2100.  Presum- 
ably by  that  time  we  shall  have  learned  much  more 
than  we  now  know  about  intensive  methods  of  food 
production. 

Let  us  take  one  simple  instance  only.  In  the 
United  States  we  are  substituting  gasoline-driven 
farm  machinery  for  horse  power  in  agricultural  work. 


222  THE  SOCIAL  LIFE  OF  ANIMALS 

The  land  required  to  produce  feed  for  one  horse 
will  equally  well  provide  food  for  a  man.  Baker, 
the  agricultural  economist  cited  earlier,  estimates 
that  the  land  released  annually  by  this  change  in 
farm  technique  can  be  turned  to  growing  human 
food  almost  as  fast  as  our  population  is  increasing. 

The  question  seems  rather  one  of  adequate  food 
distribution  than  of  shortage  of  food.  Under  con- 
ditions which  we  can  visualize  at  present  there  seems 
little  likelihood  of  a  real  food  shortage  for  the  world 
as  a  whole. 

If,  however,  these  conclusions  prove  to  be  com- 
pletely wrong,  and  the  world  population  is  now  or 
will  become  too  high  by  biological  standards,  there 
is  still  the  question  as  to  whether  war  is  a  sound 
and  sufficient  means  of  controlling  population 
growth.  The  theory  that  war  is  an  efficient  means 
of  stopping  the  increase  of  mankind  is  so  contrary 
to  fact  that  I  allow  myself  to  say  No  in  the  first 
place  and  present  the  evidence  later. 

The  immediate  effect  of  a  war  upon  the  civilian 
population  is  to  depress  the  birth  rate  and  raise  the 
death  rate  on  both  sides  of  the  line,  whether  in  the 
winning  or  the  losing  nation.  Figure  44,  taken  from 
a  study  by  Pearl  on  population  trends  during  the 
World  War,  gives  these  data  for  the  unoccupied  parts 


HUMAN    IMPLICATIONS 


223 


of  France,  for  Bavaria  and  for  England,  from  1913 
to  1918.  (92) 

In  1913  deaths  and  births  in  these  parts  of  France 
were  almost  equal;  in  1918  there  were  approximately 


)fT/iR 


Fig.  44.  The  percentage  which  deaths  were  of  births 
steadily  increased  during  the  war  years  in  France  (non- 
invaded  departments),  Prussia,  Bavaria,  England  and 
Wales.  (From  Pearl.) 

two  deaths  for  each  birth.  In  Bavaria,  in  1913,  there 
were  five  births  for  every  three  deaths;  in  1918  there 
were  three  births  for  every  four  deaths.  The  trend 
lines  in  Figure  44  for  these  two  countries  run 
almost  parallel,  though  France  was  invaded  and  los- 
ing in  much  of  the  fighting  while  Bavaria  was  free 
from  foreign  troops  and  part  of  a  winning  nation 
until  near  the  end.  As  usual,  analysis  of  such  a  situ- 
ation is  not  simple.  Bavaria,  although  enjoying  the 


224  THE  SOCIAL  LIFE   OF  ANIMALS 

psychological  advantage  of  belonging  apparently  to 
the  winning  side,  suffered  the  physiological  disad- 
vantage of  an  increasingly  severe  food  shortage,  while 
France  averaged  an  adequate  food  ration.  In  Eng- 
land during  the  same  time,  where  there  was  neither 
invasion  nor  starvation,  there  was  the  same  tendency 
toward  increase  of  deaths  in  proportion  to  births, 
though  less  marked.  These  statistics,  of  course,  do 
not  take  into  account  the  almost  unprecedented 
death  rates  in  the  fighting  lines. 

Temporarily  the  population  growth  was  checked, 
but  almost  immediately  following  the  close  of  the 
war  the  ratio  of  births  to  deaths  resumed  their  pre- 
war trend  lines.  Pearl,  writing  in  1921,  (93)  summed 
up  his  study  in  these  words:  "Those  persons  who  see 
in  war  and  pestilence  any  absolute  solution  of  the 
world  problem  of  population  .  .  .  are  optimists  in- 
deed. As  a  matter  of  fact,  all  history  tells  us,  and  re- 
cent history  fairly  shouts  in  its  emphasis,  that  such 
events  make  the  merest  ephemeral  flicker  in  the 
steady  onward  march  of  population  growth." 

Fifteen  years  later,  in  1936,  (94)  Pearl  again  wrote, 
alluding  particularly  to  the  effects  of  wars  of  con- 
quest by  one  nation  to  acquire  the  territory  of  an- 
other: "The  world  problem  of  population  and  area, 
however,  remains  unaltered  in  theory,  though  prac- 
tically it  will  have  been  made  worse  because  of  the 


HUMAN    IMPLICATIONS  225 

extravagantly  wasteful  destruction  of  real  wealth  that 
war  always  causes.  This  is  the  problem  that  is  really 
serious— how  can  forty  persons  be  maintained  for 
every  square  mile  of  land  surface  of  the  globe- 
good,  bad  and  indifferent  land  together?  War  can- 
not enlarge  the  land  surface  that  must  support  man- 
kind; it  has  never  diminished  the  total  number  of 
people  who  want  to  live  on  it  except  by  a  tiny  frac- 
tion for  quite  a  brief  period.  There  is  no  way  out 
of  the  dilemma  by  the  pathway  of  war." 

It  is  a  comparatively  new  idea  that  population  can 
be  controlled  at  all  except  by  famine,  pestilence, 
and  war,  which  have  been  regarded  as  acts  of  God. 
Acts  of  God  or  not,  we  can  no  longer  tolerate  famine 
or  pestilence  if  we  have  the  power  to  prevent  them; 
and  lacking  such  power  we  intend  to  get  it  as  soon 
as  it  is  humanly  possible.  Among  dispassionate,  ex- 
pert students,  war  has  similarly  lost  caste  as  a  means 
of  population  control,  though  the  man  in  the  street 
has  not  yet  learned  this. 

Instead  of  the  dubious  check  these  agencies  fur- 
nished there  is  a  steady  turning  to  birth  control, 
even  in  the  countries  where  it  is  most  surprising  to 
find  this.  In  Germany  and  Italy,  although  artificial 
stimuli  are  being  applied  to  keep  up  the  birth  rate, 
some  kind  of  birth  control  evidently  is  occurring. 

There    is    significance    not    only    in    the    average 


226  THE  SOCIAL  LIFE  OF  ANIMALS 

density  of  people  per  square  mile  of  the  earth's  sur- 
face, but  also  in  the  population  density  of  the  most 
crowded  nations.  The  degree  of  crowding  in  cer- 
tain countries  with  whose  problems  we  are  familiar 
is  shown  in  the  following  list.  The  figures  given  are 
slightly  rounded  statements  of  the  average  popula- 
tion density  per  square  mile  of  land  territory.  The 
most  densely  populated  countries  of  the  world  are 
listed  here  in  order  (94): 


COUNTRY 

PEOPLE  PER  SQUARE  MILE 

1.  Belgium 

700 

2.  England  and  Wales 

680 

3.  Netherlands 

660 

4.  Japan 

450 

5.  Germany 

360 

6.  Italy 

360 

7.  China  (proper) 

300 

8.  Czechoslovakia 

270 

For  many  purposes  it  is  hardly  fair  to  compare 
the  relatively  small  countries  like  Belgium  and  the 
Netherlands  with  others  like  Japan  or  Italy  which 
are  larger  but  contain  a  high  percentage  of  waste 
land.  For  our  purposes,  however,  the  list  as  it  stands 
is  fair  enough;  such  data  represent  the  facts  we  have 
to  face. 

At  present  about  two  and  a  half  acres  are  required 


HUMAN    IMPLICATIONS  227 

to  supply  food  to  one  person,  if  the  soil  is  fair  to 
good  and  the  husbandry  is  good  according  to  present 
standards.  This  means  that  under  modern  condi- 
tions of  agriculture  the  upper  limit  of  a  relatively 
self-contained  population  is  about  250  people  per 
square  mile.  It  will  be  seen  that  Belgium  with  its 
700  per  square  mile  almost  triples  this  upper  limit, 
and  that  England  and  Wales  and  the  Netherlands 
more  than  double  it.  Such  high  population  densities 
can  be  supported  by  trade  conducted  with  other 
countries  on  a  large  scale.  They  could  also,  as  we 
have  seen  earlier,  be  supported  by  improved  meth- 
ods of  agriculture.  An  Italian  expert  on  populations 
said  in  my  hearing  some  years  ago  that  population 
pressure  is  not  a  direct  cause  for  war,  but  can  be 
used  by  a  clever  leader  to  range  a  nation  behind 
aggressive  policies  which  lead  to  war.  In  the  short 
run  that  is  easier  than  to  educate  people  to  apply 
the  available  knowledge  which  would  allow  Italy, 
for  example,  to  feed  her  present  population,  and 
more,  from  the  products  of  her  own  soil. 

It  is  time  now  to  turn  to  the  second  of  the  ques- 
tions concerning  the  biological  background  of  war. 
In  the  light  of  the  preceding  discussion  we  can  re- 
state this  question  as  follows:  Although  underlying 
biological  relationships  do  not  necessarily  lead  to 


228  THE  SOCIAL  LIFE  OF  ANIMALS 

war,  is  not  war  biologically  justified  by  the  results 
produced? 

If  war  does  benefit  the  race  in  distinct  and  unique 
ways,  then  the  biologist  must  favor  a  system  of  so- 
ciety which  will  bring  about  the  proper  kind  and 
the  correct  number  of  wars  to  produce  the  best  racial 
selection.  If  war,  on  the  other  hand,  tends  toward 
human  deterioration  then  the  biologist  must  oppose 
a  system  of  international  relations  based  on  war. 
Again  it  is  a  question  of  evidence. 

The  matter  of  individual  biological  selection  is 
one  that  is  fairly  obvious  even  to  the  layman;  and 
his  conclusion  that  the  direct  results  of  war  are  harm- 
ful biologically  has  been  well  supported  by  scientists 
whose  interest  in  the  subject  is  more  inclusive  than 
their  natural  sympathy  for  the  young  men  of  their 
acquaintance  who  have  incurred  wounds  or  have 
been  gassed  or  have  suffered  severely  from  some  of 
the  typical  wartime  epidemic  diseases.  The  work  of 
David  Starr  Jordan  before  1914  is  classic;  (70,  71, 
73)  but  the  evidence  furnished  by  the  World  War  is 
more  important  to  us.  American  experience  at  that 
time  is  best  set  forth  in  the  slender  book  by  Professor 
Harrison  Hunt  (67)  of  Michigan  State  College,  who 
studied  the  records  of  the  American  army,  using  mod- 
ern statistical  methods. 

He  was  left  with  no  doubt  that  war  selects  the 


HUMAN    IMPLICATIONS  229 

best  of  our  young  men  for  exposure  to  wartime  haz- 
ards. We  have  space  for  one  bit  of  evidence.  Hunt 
found  that  for  the  drafted  American  army,  83  per 
cent  of  the  mentally  defective  were  rejected;  those 
of  normal  mentality  and  the  17  per  cent  who  were 
only  slightly  subnormal  were  held  for  service.  A 
good  geneticist  would  have  reversed  the  procedure, 
sending  the  mentally  deficient  out  into  wartime  risks 
and  keeping  the  others  at  home  to  continue  the 
race.  But  this  is  so  contrary  to  fact  in  all  the  stand- 
ards by  which  armies  are  selected  that  it  seems  faintly 
ridiculous  in  the  telling.  Personal  selection,  so  far  as 
it  exists  in  modern  warfare,  selects  the  individual  to 
be  killed  or  wounded  because  he  is  physically  or 
mentally  superior  to  those  who  are  left  at  home.  (64) 
The  ill  effects  of  this  selection  among  the  young 
men  are  evident  in  a  nation  where  war  losses  have 
been  heavy,  but  they  are  less  drastic  for  people  as 
a  whole  than  they  might  be  if  it  were  not  for  various 
mitigating  factors.  To  date  only  half  the  race  has 
suffered  in  so-called  civilized  warfare,  since  women 
have  been  exempt  from  actual  combat.  Also  many 
young  men  return  who,  though  wounded  and  per- 
haps otherwise  handicapped,  are  still  physically  ca- 
pable of  passing  on  their  gerra  plasm  to  succeeding 
generations.  And  even  in  populations  badly  shattered 
by  war  most  of  these  genetic  ill  effects  could  be  ob- 


230  THE  SOCIAL   LIFE   OF  ANIMALS 

viated  if  monogamy  were  less  of  an  ingrained  human 
practice. 

The  effects  of  severe  wartime  epidemics,  which 
are  usually  the  cause  of  more  deaths  than  the  actual 
fighting,  are  subject  to  the  same  comments;  but  with 
these  epidemics  the  civilian  population  is  also  di- 
rectly affected,  as  was  the  case  with  the  influenza 
pandemic  that  swept  the  world  in  1918,  and  carried 
off  in  a  day  more  civilians  than  did  many  spectacu- 
lar air  raids  combined. 

General  epidemics  tend  to  fall  most  heavily  on 
the  old  and  the  young;  biologically  we  are  most  in- 
terested in  the  fate  of  children  and  young  people. 
Disease  and  undernourishment  drastically  reduced 
the  younger  population  in  places  well  away  from  the 
fighting  lines  in  the  last  war.  Homer  Folks,  (47)  U.  S. 
Red  Cross  commissioner,  testifies  that  in  some  sec- 
tions of  Italy  60  per  cent  of  the  children  failed  to 
survive  wartime  conditions.  The  children  of  Ger- 
many and  of  Poland  suffered  greatly. 

If  he  could  know  that  such  severe  exposure  elimi- 
nated the  relatively  weaker  specimens  and  left  a 
stronger,  hardier  race,  the  biologist  could  reconcile 
himself  to  the  death  of  these  children,  though  emo- 
tionally he  might  rebel. 

But  this  rationalization  is  impossible.  Study  of  the 
after-effects  of  epidemics  upon  children   (45)   does 


HUMAN    IMPLICATIONS  23  1 

not  show  a  group  of  sturdy  survivors,  with  all  the 
weaklings  eliminated.  Rather,  the  later  history  of 
these  children  shows  that  they  have  a  lower  resistance 
to  the  next  severe  disease  that  strikes  them.  Ap- 
parently many  such  children,  though  surviving,  are 
weakened  for  some  years  thereafter. 

Similarly,  the  children  back  of  the  battle  lines  in- 
clude many  whose  experience  left  a  mark,  and  who 
recover  only  slowly  from  its  injurious  effects.  They 
were  not  a  selected  lot,  and  their  own  generation 
has  suffered.  Fortunately  all  our  evidence  indicates 
that  those  who  survived  are  able  to  pass  on  their 
inherited  qualities  unimpaired  to  their  children;  but 
many  are  unable  to  provide  for  their  families  the 
physical  care  and  conditions  for  living  which  make 
for  the  fullest  development  of  inherited  potentiali- 
ties. 

Perhaps  a  sane  and  cautious  quotation  from  Pro- 
fessor Holmes  of  California  will  be  a  fitting  sum- 
mary for  this  section.  In  1921,  Holmes  wrote:  (63) 
**On  the  whole  it  is  quite  probable,  I  believe,  that 
the  effect  of  military  selection  is  harmful.  ...  It  is 
a  matter  of  serious  doubt  whether  the  beneficial  fac- 
tors come  near  outweighing  the  adverse  selection  of 
battles." 

What  are  some  of  the  beneficial  effects  which  this 
statement  suggests  may  exist?  One  of  them  is  that 


232  THE  SOCIAL   LIFE   OF   ANIMALS 

war  is  necessary  to  maintain  racial  vigor.  This  is  a 
matter  on  which  statistics  are  not  available,  and  on 
which  personal  opinion  must  play  as  reasonable  a 
part  as  it  can. 

To  me  it  seems  a  misreading  of  history  that  leads 
to  the  justification  of  war  as  a  means  of  keeping  up 
the  vigor  of  the  race.  I  should  say,  rather,  that  wars 
have  frequently  revealed  the  loss  of  racial  or  national 
vigor  among  a  people  made  soft  by  easy  living,  which 
in  turn  had  been  made  possible,  at  least  at  times,  by 
a  long  series  of  successful  wars  of  conquest. 

Anyone  who  attempts  to  maintain  the  thesis  that 
wars  do  keep  racial  stocks  vigorous— and  there  are 
biologists  who  believe  this— is  troubled  by  the  Chinese 
people.  This  much-discussed  and  frequently  invaded 
land  was  populated  by  the  forerunners  of  the  pres- 
ent Chinese  during  the  days  when  Egypt,  Assyria, 
Babylon,  Greece  and  Persia,  to  name  no  more,  were 
fighting  the  wars  recorded  in  our  general  histories. 
Those  warlike  peoples  have  lost  their  racial  vigor 
but  the  Chinese,  who  have  been  relatively  peaceful, 
have  retained  it.  This  stumbling  block  cannot  be 
removed  by  denying  racial  vigor  to  the  Chinese;  they 
have,  in  the  past,  absorbed  too  many  temporary  con- 
querors, and  have  occupied  and  are  occupying  by 
peaceful  penetration  too  much  of  the  earth's  terri- 
tory, to  be  dismissed  as  a  racially  decadent  people. 


HUMAN    IMPLICATIONS  233 

There  are  anthropologists  who  reckon  them  biologi- 
cally the  most  advanced  people  living  today. 

There  is  another  allied  but  somewhat  different 
theory  regarding  the  human  benefits  conferred  by 
war  which  holds  that  even  though  in  direct  personal 
selection  the  war  system  is  dysgenic,  it  does  tend  to 
select  the  fittest  races  and  nations  for  survival.  This 
theory  is  usually  applied  to  European  history,  w^here 
in  the  long  struggle  of  advanced  European  nations 
against  backward  poorly-equipped  natives  of  Amer- 
ica, Asia,  Australia  and  Africa,  victory  has  eventu- 
ally rested  with  the  Europeans.  Whatever  the  in- 
trinsic human  merits  of  the  case,  a  question  on  which 
Hindus  may  disagree  with  Englishmen,  there  can  be 
no  doubt  that  such  conflicts  have  been  won  by  the 
nation  which  possesses  the  more  modern  social  or- 
ganization and  the  better  gadgets  with  which  to 
fight;  and  the  winning  nation  has  not  hesitated  to 
levy  on  the  weaker  one  for  whatever  of  its  posses- 
sions and  services  it  could  utilize  for  its  own 
advantage. 

When,  however,  one  European  nation  fights  an- 
other, as,  for  example,  France  and  Germany,  who 
can  maintain  that  the  nation  that  won  at  Waterloo 
and  in  1918  is  superior  to  the  people  who  won  at 
Leipzig  and  Sedan?  Or,  to  come  closer  home,  does 
the  fact  that  the  Confederacy  lost  the  war  between 


234  THE  SOCIAL   LIFE   OF  ANIMALS 

the  States  prove  that  the  white  people  of  the  South 
are  racially  inferior  to  those  of  the  North? 

Actually,  of  course,  we  are  not  fighting  racial  wars 
at  present.  What  race  won  the  World  War,  or  for 
that  matter,  lost  it?  Modern  warfare  among  so-called 
civilized  powers  probably  does  result  in  victory  for 
superior  wealth,  better  organization,  shrewder  propa- 
ganda, and  other  social  achievements,  but  we  have 
little  good  evidence  to  link  these  social  attributes 
with  racial  stock,  in  spite  of  contemporary  German 
determination  to  assume  the  connection. 

Let  us  allow  Popenoe  and  Johnson,  (99)  recog- 
nized students  of  eugenics,  to  summarize  this  whole 
inquiry  into  the  biological  justification  of  war.  Writ- 
ing in  1918,  when  the  subject  was  near  the  top  of 
men's  minds,  they  said:  "When  the  quality  of  the 
combatants  is  so  high  compared  with  the  rest  of  the 
world  as  during  the  Great  War,  no  conceivable  gains 
can  offset  the  loss.  It  is  probably  well  within  the  facts 
to  assume  that  the  period  of  the  late  war  represents 
a  decline  in  inherent  human  quality  greater  than 
in  any  similar  length  of  time  in  the  previous  his- 
tory of  the  world." 

It  seems  to  me  that  such  evidence  and  reasoning  as 
I  have  presented  indicates  pretty  clearly  that  the 
present  system  of  international  relations  is  biologi- 
cally unsound.  Attempts  which  have  been  made  in 


HUMAN    IMPLICATIONS  235 

the  past  to  lend  biological  respectability  to  the  pres- 
ent system  by  regarding  it  as  an  expression  of  an 
inevitable  struggle  for  existence  have  overlooked  not 
only  its  defects  as  a  selecting  agent  but,  more  serious, 
have  often  not  even  been  conscious  of  the  existence 
of  another  fundamental  biological  principle,  that  of 
co-operation.  Is  it  possible  to  envisage  a  system  of 
international  relations  which  will  be  fairly  based  on 
both  these  aspects  of  biology? 

One  of  the  first  questions  to  be  examined  is  that 
of  the  size  of  the  co-operating  unit  practicable  in 
such  a  system.  It  is  possible  to  make  a  case  for  the 
present  human  social  divisions,  where  nations  of  var- 
ious size  co-operate  within  their  own  boundaries 
though  competing  with  each  other  for  various  types 
of  supremacy.  Within  each  of  these  nations  are 
graded  series  of  groupings  in  great  variety,  which 
also  co-operate  within  and  compete  across  their  tan- 
gible or  intangible  boundaries.  Here  immediately 
we  come  across  an  important  qualitative  difference 
in  the  competition.  Within  each  nation  this  inter- 
group  struggle  is  normally  carried  on  by  approxi- 
mately peaceful  and  orderly  means.  By  contrast  it 
is  accepted  that  the  competition  across  national 
limits,  usually  peaceful  and  orderly,  may  at  any  time 
break  down  into  the  socially  backward  phenomenon 
called  war;  and  even  in  periods  of  peace  and  social 


236  THE  SOCIAL   LIFE   OF  ANIMALS 

progress  much  of  the  average  nation's  energy,  wealth 
and  forethought  is  diverted  to  preparing  for  the  next 
war. 

Peaceful  intergroup  competition  within  a  nation 
has  come  to  rest,  in  the  first  place,  on  habit,  prefer- 
ence and  a  realization  that  only  temporarily  is  an 
advantage  gained  by  violence;  and,  in  the  second 
place,  on  a  government,  often  set  up  by  mutual  con- 
sent of  the  competing  groups,  which  is  strong  enough 
to  block  or  stop  cruder  appeals  to  force,  and  which 
is  expected  by  them  to  do  so. 

The  suggestion  has  been  urgently  repeated  since 
the  time  of  Sully,  (61)  the  great  minister  of  Henry 
of  Navarre  and  France,  that  there  should  be  a  simi- 
lar international  organization.  Theoretically  there  is 
almost  everything  to  be  said  for  this  proposal.  Such 
an  international  organization  might  be  set  up  much 
as  the  federal  government  of  our  country  was 
planned,  to  supervise  the  functioning  of  the  differ- 
ent states.  This  system  calls  for  representative  gov- 
ernment, a  relatively  unbiased  court  of  final  judicial 
appeal,  and  certain  potential  police  power,  which  in 
our  American  experience  has  been  used  but  rarely 
on  a  national  scale. 

The  present  League  of  Nations,  even  in  its  most 
hopeful  days,  did  not  show  more  than  remote  pos- 
sibilities of  equaling  on  a  world  scale  what  the  British 


HUMAN    IMPLICATIONS  237 

Empire  has  done  fairly  adequately  of  recent  years 
for  more  than  one-fourth  of  the  earth's  land  area. 
Any  future  international  body  which  will  undertake 
to  apply  the  balanced  principles  of  struggle  and  co- 
operation on  a  global  basis  must,  among  its  other 
qualifications,  avoid  certain  outstanding  mistakes  of 
the  present  League. 

It  cannot  be  really  co-operative  if  it  is  basically  a 
league  of  victor  nations  formed  to  administer  a  puni- 
tive peace  treaty,  for  this  is  hardly  a  step  in  advance 
of  the  time-honored  national  alliances  for  defense 
and  offense,  which  are  co-operative  only  to  be  de- 
structive. It  must  not  be  dominated  in  any  depart- 
ment by  the  representatives  of  any  one  nation,  not 
even  when  that  nation  is  as  intelligently,  and  shall 
I  say  selfishly,  benevolent  as  England  and  its  domin- 
ions today.  It  must  be  so  organized  as  to  secure  and 
hold  adherence  from  the  great  majority  of  nations. 
As  a  step  toward  this  end,  the  biologist's  international 
system  must  be  a  dynamic  organization  capable  of 
and  designed  to  effect  changes  rather  than  set  up 
to  preserve  any  given  status  quo,  regardless  how 
favorable  for  the  predominant  powers. 

Biology  teaches  the  inevitability  of  change,  if  it 
teaches  anything.  We  must  have  some  device  in  our 
system  which  will  allow  for  needed  changes,  some 
means  of  making  those  compromises  at  which  the 


238  THE  SOCIAL   LIFE   OF  ANIMALS 

English  and  the  French  are  so  proficient  in  their  in- 
ternal affairs.  In  international  as  in  legal  circles,  we 
must  have  some  peaceful  means  of  declaring  a  de- 
funct nation  to  be  in  fact  bankrupt  or  unable  to 
manage  its  own  business,  and  to  distribute  its  assets 
among  the  proper  creditors. 

When  such  a  system  is  installed  there  will  need 
to  be  not  only  the  means  for  international  consulta- 
tion, and  a  hearing  for  the  troubles  of  the  world; 
there  will  also  be  the  necessity  for  courts  of  inter- 
national justice.  One  of  these  may  well  grow  out  of 
the  present  World  Court  at  Geneva,  patterned  on 
the  Supreme  Court  of  this  country;  another  might 
be  a  development  of  the  international  court  of  arbi- 
tration which  has  been  located  for  many  years  at 
The  Hague. 

At  this  point  we  come  to  a  serious  divergence  of 
opinion.  Should  these  courts  be  supported  by  police 
power?  As  a  realistic  biologist  it  seems  to  me  that  in- 
ternational police  force  will  probably  be  a  necessity 
in  those  cases  when  a  nation  or  a  section  of  a  nation 
attempts  to  raise  itself  in  the  peck-order  of  govern- 
ments by  direct  action  rather  than  waiting  for  the 
results  of  the  more  just  but  slower  pressure  of  world 
opinion.  Much  of  the  police  activities  should  be 
limited  to  such  duties  as  are  now  exercised  by  our 
federal  marshals,  but  in  my  judgment  there  would 


HUMAN    IMPLICATIONS  239 

need  to  be  the  possibility  of  the  use  of  even  stronger 
police  pressure. 

But  it  is  certain  that  if  an  international  organiza- 
tion is  to  succeed,  police  power  must  be  used  very 
rarely.  The  attempts  of  the  British  government  to 
coerce  the  American  colonies  or  the  Irish  people  are 
conspicuous  as  a  demonstration  of  the  frequent  fail- 
ure of  massed  force  to  compose  complex  human 
maladjustments.  It  is  noteworthy  that  such  enforce- 
ment has  not  been  used  in  the  long  and  successful 
operation  of  our  own  Supreme  Court. 

Practically,  it  is  possible  that  nations  will  join  in 
an  international  enterprise  which  is  limited  to  con- 
sultation and  judicial  review  of  all  disputes  long  be- 
fore they  will  relinquish  any  other  phase  of  their 
jealously  guarded  sovereignty  to  such  an  interna- 
tional organization.  We  may  even  be  able  to  work 
out  a  method  of  international  co-operation  based 
entirely  on  patience,  wisdom  and  justice,  though  in 
the  light  of  past  experience  this  seems  at  present 
unlikely. 

Such  a  world  organization  will  never  be  perfect. 
Man  is  not.  Neither  is  the  government  of  Chicago,  of 
Illinois,  of  our  United  States.  And  yet  who  would 
not  prefer  to  live  in  Chicago,  even  back  in  the  gang- 
ster era  of  the  nineteen-twenties,  rather  than  in  the 
period  of  greater  individual  freedom  for  privileged 


240  THE  SOCIAL   LIFE  OF  ANIMALS 

people  that  London  or  Paris  of  the  Middle  Ages 
afforded? 

A  thoughtful  and  sincere  biologist  may  object  that 
the  world  is  too  large  an  area  for  a  successful  co- 
operative unit;  that  we  need  units  intermediate  in 
size  to  allow  for  human  evolution  those  advantages 
which  Professor  Wright  has  demonstrated  for  popu- 
lations intermediate  in  size.  To  such  objection  one 
must  reply  that,  as  to  the  latter  point,  the  main- 
tenance of  smaller  co-operative  and  competing  units 
within  the  larger  one  is  part  of  the  scheme  as 
sketched.  And  to  the  first,  that  of  the  great  size  of 
the  earth,  it  needs  only  to  be  mentioned  that  thanks 
to  recent  improvements  in  transportation  facilities. 
New  York  is  in  point  of  time  as  near  the  Orient  as 
it  was  to  Los  Angeles  in  1885;  and  there  are  few 
places  on  the  globe  as  remote  from  Washington  as 
was  San  Francisco  before  the  Union  Pacific  Railway 
was  built.  In  transportation  and  communication,  and 
in  community  of  essential  human  interests,  the  world 
is  ripe  for  a  workable  international  organization. 

From  the  standpoint  of  pure  biology,  disregarding 
considerations  that  may  seem  to  smack  of  the  social 
sciences,  the  mortal  enemies  of  man  are  not  his  fel- 
lows of  another  continent  or  race;  they  are  the  aspects 
of  the  physical  world  which  limit  or  challenge  his 
control,  the  disease  germs  that  attack  him  and  his 


HUMAN    IMPLICATIONS  24 1 

domesticated  plants  and  animals,  and  the  insects  that 
carry  many  of  these  germs  as  well  as  working  notable 
direct  injury.  To  the  biologist  this  is  not  even  the 
age  of  man,  however  great  his  superiority  in  size 
and  intelligence;  it  is  literally  the  age  of  insects. (7) 

This  is  a  fact  which  must  have  repeated  emphasis. 
In  the  tropics  there  is  only  the  narrow  strip  along 
the  Panama  Canal  and  similar  small  areas  in  which 
man  has  shown  the  ability  to  compete  successfully 
with  the  insects;  and  the  techniques  of  this  competi- 
tion are  too  expensive  as  yet  to  apply  along  the  vast 
rich  stretches  of  the  Orinoco  River,  the  Amazon  or 
Congo;  there,  undoubtedly,  the  insects  are  in  con- 
trol. In  countries  like  India  and  Russia  mosquito- 
borne  malaria  is  a  plague  which  saps  the  energy  of 
those  enormous  populations  as  it  does  today  in  our 
own  South. 

There  are  good  biological  precedents  for  such 
competition  between  different  types  of  organisms  as 
that  between  man  and  insects  or  betw^een  man  and 
bacteria.  In  fact,  with  almost  negligible  exceptions, 
the  only  kind  of  mass  slaughter  for  which  there  is 
precedent  in  animal  biology  is  found  in  interspecific 
struggles.  One  species  of  animal  may  destroy  another 
and  individuals  may  kill  other  individuals,  but  group 
struggles  to  the  death  between  numbers  of  the  same 


242  THE  SOCIAL  LIFE  OF  ANIMALS 

species,  such  as  occur  in  human  warfare,  can  hardly 
be  found  among  non-human  animals. 

These  techniques  by  which  we  can  successfully 
combat  our  enemies,  the  insects,  and  the  viruses  they 
transport  are  too  expensive  for  the  world  today. 
They  are  too  expensive  because  even  the  peaceful 
nations  are  using  so  much  of  their  resources  for  buy- 
ing and  building  armament  on  an  unprecedented 
scale,  apparently  to  make  one  more  experimental  test 
of  the  fact  that  war  is  biologically  indefensible. 

In  our  struggles  with  our  physical  environment, 
with  disease  germs  and  insects,  we  have  ample  op- 
portunity for  the  struggle  for  existence,  and  stimu- 
lus enough  to  apply  to  the  limit  the  principle  of 
co-operation. 

Unconsciously  or  consciously,  the  innate  urge  to- 
ward co-operation  appears  even  under  circumstances 
where  it  would  seem  least  likely  to  be  fostered. 

Even  in  the  most  seriously  war-torn  countries,  as 
in  Spain  today,  when  one  is  withdrawn  from  the  ac- 
tual scene  of  battle  one  finds  the  common  people  en- 
gaged as  best  they  can  in  their  normal  activities  of 
providing  food,  clothing  and  shelter  for  themselves 
and  their  families,  with  the  ineradicable  drive  to- 
ward constructive  co-operation  that  we  have  found 
evident  throughout  the  animal  kingdom.  Such  co- 
operative activity  will  reach  through  a  family,  from 


HUMAN    IMPLICATIONS  243 

family  to  family,  from  city  to  city  and  even  across 
frontiers. 

These  normal  activities  can  be  wiped  out  in  a  few 
minutes  by  the  exaggerated  expression  of  the  struggle 
for  existence  which  we  call  war,  extended  beyond 
all  biological  justification  and  become,  as  Malinowski 
has  said,  "nothing  but  an  unmitigated  disease  of 
civilization."  (78) 

It  is  a  disease  of  long  standing  which  even  under 
most  favorable  conditions  we  must  not  expect  to 
see  cured  overnight;  but  the  outlook  is  not  without 
hope.  There  seems  to  be  no  inherent  biological  rea- 
son why  man  cannot  learn  to  extend  the  principle  of 
co-operation  as  fully  through  the  field  of  interna- 
tional relations  as  he  has  already  done  in  his  more 
personal  affairs.  In  addition  to  the  unconscious  evo- 
lutionary forces  that  play  on  man  as  well  as  on  other 
animals,  he  has  to  some  extent  the  opportunity  of 
consciously  directing  his  own  social  evolution.  Un- 
like ants  or  chickens  or  fishes,  man  is  not  bound 
over  to  form  castes  or  peck-orders  or  schools,  or  to 
wait  for  a  reshuffling  of  hereditary  genes  before  he 
can  discontinue  behavior  which  tends  toward  the 
destruction  of  his  species. 


VIII. 


Social  Transitions 


WHEN  DOES  an  animal  group  become  truly  social? 
This  question  has  already  arisen  in  preceding  chap- 
ters and  is  difficult  for  a  thoughtful  biologist  to  an- 
swer with  confidence. 

One  school,  now  happily  small,  regards  society  as 
beginning  when  animals  first  display  a  social  in- 
stinct. (16)  By  this  they  probably  mean  that  social 
animals  have  inherited  a  behavior  pattern  that 
causes  them  to  live  together  with  others  of  their  kind 
in  more  or  less  closely  co-operative  units.  Others 
consider  that  animals  are  social  when  they  carry  on 
group  life  in  which  there  is  clear  evidence  of  a  divi- 
sion of  labor.  (42)  There  is  also  the  frequent  sug- 
gestion that  only  those  animals  are  truly  social  whose 
behavior  is  an  extension,  directly  or  indirectly,  of 
familial  behavior.  (119) 

For  myself,  I  regard  those  groups  in  which  ani- 
mals confer  distinct  survival  values  upon  each  other 
as  being  at  least  partially  social;  this  is  the  concep- 
tion that  has  most  often  appeared  in  these  pages.  (3) 

244 


SOCIAL   TRANSITIONS  245 

And  from  a  still  different  point  of  view,  those  who 
would  stretch  the  idea  of  social  living  rather  widely 
would  say,  as  I  have  indicated  in  Chapter  V,  that 
when  animals  behave  differently  in  the  presence  of 
others  than  they  would  if  alone,  they  are  to  that 
extent  social.  (115) 

These  ideas  concerning  what  constitutes  a  proper 
definition  of  animal  societies,  while  not  necessarily 
mutually  exclusive,  are  sufficiently  different  to  raise 
difficulties  when  one  tries  to  examine  critically  the 
useful  general  concept  of  social  life;  it  will  be  profit- 
able to  study  some  of  them  separately. 

As  to  the  first  definition,  that  social  life  must  be 
limited  to  those  animals  that  possess  a  social  instinct, 
an  inherited  behavior  pattern,  it  is  hard  to  demon- 
strate beyond  reasonable  doubt  that  many  patterns 
of  social  behavior  are  in  fact  inherited.  Is  the 
tendency  of  many  fishes  to  form  closely-knit  schools 
inherited  or  an  early-conditioned  bit  of  behavior? 
There  is  some  evidence  that  it  is  inherited,  but  we 
are  not  yet  sure  of  it.  But  if  it  were  granted  that 
such  schooling  tendencies  are  innate,  it  would  not 
necessarily  follow  that  they  are  instinctive.  There  are 
different  degrees  of  complication  of  inherited  be- 
havior patterns,  from  the  relatively  simple  reflex  ac- 
tion of  an  unborn  embryo  to  the  complex  mating 
behavior  shown,  for  example,  by  some  insects  and 


246  THE  SOCIAL  LIFE  OF  ANIMALS 

by  rats.  The  exact  determination  of  the  place  in  this 
line  of  increasing  complexity  at  which  an  action 
ceases  to  be  a  simple  reflex  and  becomes  a  more 
elaborate  tropism,  or  the  point  at  which  the  tropism 
gives  way  to  an  instinct,  has  never  been  made.  That 
is,  we  do  not  know  just  how  far  down  in  develop- 
ing patterns  instinctive  behavior  extends. 

There  is  the  added  complication  that  the  word 
"instinct"  has  been  loosely  used.  The  most  workable 
definition  that  I  have  arrived  at  is  a  modification  of 
an  older  one  of  Wheeler's:  An  instinct  is  a  com- 
plicated reaction  which  an  animal  gives  when  it  re- 
acts as  a  whole  and  as  a  representative  of  a  species 
rather  than  as  an  individual,  which  is  not  improved 
by  experience,  and  which  has  an  end  or  purpose  of 
which  the  animal  cannot  be  aware.  Too  frequently 
the  word  has  been  applied  to  any  bit  of  behavior 
whose  origin  and  motivation  the  observer  did  not 
understand,  with  the  unfortunate  paradoxical  im- 
plications that  thereby  the  action  was  explained  and 
at  the  same  time  could  not  be  further  explained. 
As  a  result  of  this  uncritical  usage  many  careful 
workers  disapprove  employing  the  word  under  any 
conditions,  and  particularly  in  the  field  of  social 
activities. 

In  recent  years  some  students  of  social  life  have 
attempted  to  avoid  the  term  "social  instinct,"  while 


SOCIAL   TRANSITIONS  247 

employing  the  same  fundamental  idea  under  the 
thin  disguise  of  "social  appetite,"  (122)  "social  drive," 
or  "group  interattraction,"  (100)  which  is  apparently 
understood  as  inherited.  These  contributions  to  a 
more  picturesque  language  do  not  necessarily  ad- 
vance our  understanding  of  social  behavior. 

Still  others  sincerely  believe  that  fiehavior  patterns 
are  not  inherited,  which  seems  to  me  a  clearly  un- 
tenable position.  But  however  strong  my  belief  in 
the  actual  inheritance  of  social  behavior  I  do  not 
consider  it  helpful  to  make  the  possession  of  such  an 
inheritance  the  major  criterion  of  social  living;  it 
is  not  a  practical  working  test  as  to  what  constitutes 
social  life. 

If  division  of  labor  be  used  as  a  touchstone  the 
same  type  of  difficulty  arises.  We  do  not  know  how 
to  determine  when  such  a  division  becomes  suffi- 
ciently general  to  merit  being  called  a  social  attribute 
in  the  stricter  sense  in  which  we  are  now  using  the 
term.  For  example,  there  is  a  division  of  labor  which 
is  associated  with  sex  and  which  is  almost  as  exten- 
sive as  sex  itself.  When  does  this  particular  division 
of  labor  cease  to  be  merely  an  expression  of  sex  and 
become  social  in  the  commonly  accepted  use  of  the 
word? 

The  mention  of  sex  brings  up  again  another  im- 
portant definition  of  social  life  among  animals  which 


248  THE  SOCIAL   LIFE   OF  ANIMALS 

has  already  been  listed.  This  states  that  only  those 
groups  which  have  grown  out  of  the  persistence  of 
sexual  and  more  especially  partial  or  completely 
familial  relations  are  truly  social.  This  point  of  view 
has  been  touched  upon  with  some  sympathy  in  the 
first  chapter.  There  is  an  important  relationship 
which  underlies  this  definition;  many  highly  organ- 
ized social  groups  do  develop  from  the  continuation 
and  extension  of  family  ties.  But  though  this  con- 
dition has  given  rise  to  many  of  the  better  devel- 
oped social  units,  care  must  be  taken  not  to  regard 
its  presence  as  the  essential  difference  between  the 
social  and  the  sub-social.  As  Professor  Child  (32)  has 
suggested,  boys'  gangs,  girls'  cliques,  and  men's  and 
women's  clubs  present  difficulties  to  one  who  wishes 
to  define  all  societies  as  extensions  of  familial  rela- 
tionships. It  is  quite  possible  to  regard  such  social 
phenomena  as  expressions  of  other  aspects  of  the 
social  urge  which  have  developed  independently  of 
paternal  or  fraternal  interactions.  There  are  counter- 
parts of  these  human  groups  among  other  animals, 
as  well  as  counterparts  of  the  extensions  of  family 
life.  The  overnight  aggregations  of  male  robins,  the 
long-continuing  stag  parties  of  male  deer  outside  the 
short  rutting  season,  (38)  the  flocks  of  mixed  species 
of  birds  common  in  tropical  regions  (Beebe  tells  of 
one  made  up  of  twenty-eight  individuals  represent- 


SOCIAL   TRANSITIONS  249 

ing  twenty-three  species,  (24) )  schools  of  fishes,  and 
the  swarms  of  animals  spoken  of  in  the  second  chap- 
ter, all  of  these  instances  test  and  stretch  in  varied 
ways  the  idea  that  only  those  continuing  aggrega- 
tions of  animals  which  grow  out  of  sexual  and 
familial  interrelations  are  truly  social. 

Inherited  behavior  patterns,  the  forerunners  of 
instincts,  and  sexual  differences  extend  down  to  the 
protozoa;  so  do  continuing  family  groups,  especially 
in  the  form  of  structurally  connected  colonial  or- 
ganisms. Group  survival  values  are  present  in  groups 
of  organisms  in  which  sex  has  not  yet  evolved,  as 
well  as  among  those  in  which  sex  is  elaborately  de- 
veloped. In  the  light  of  such  considerations  it  be- 
comes exceedingly  difficult  to  establish  any  one  line 
above  which  life  is  to  be  regarded  as  truly  social 
and  below  which  we  have  only  differing  degrees  of 
sub-social  relations.  Here,  as  happens  so  frequently 
in  biology,  we  are  confronted  with  a  gradual  devel- 
opment of  real  differences  without  being  able  to 
put  a  finger  with  surety  on  any  one  clearly  defined 
break  in  the  continuity.  The  slow  accumulation  of 
more  and  more  social  tendencies  leads  finally  by 
small  steps  to  something  that  is  apparently  different. 
If  we  disregard  the  intermediate  stages  the  differ- 
ence may  appear  pronounced,  but  if  we  focus  on 
these  intermediates  it  will  be  only  for  the  sake  of 


250  THE  SOCIAL  LIFE  OF  ANIMALS 

convenience  that  we  interrupt  the  connecting  chain 
of  events  at  some  comparatively  conspicuous  link 
and  arbitrarily  make  this  the  dividing  point,  when 
one  is  needed,  between  the  more  and  the  less  social. 
It  must  be  recognized  that  any  such  division  is  a 
matter  of  convenience  rather  than  a  natural  break  in 
the  development  from  mass  or  simple  group  behavior 
to  highly  evolved  social  life. 

For  our  purpose  in  the  present  account  it  is  suffi- 
cient to  recognize  that  the  well-integrated  social 
systems  of  man  and  other  mammals,  of  bird  flocks 
and  of  insect  colonies,  exhibit  among  them  the 
highest  expressions  of  social  abilities  that  have 
evolved.  In  the  range  of  social  development  shown 
in  these  animals  we  find  attributes  that  are  truly 
social  in  the  most  exclusive  use  of  the  word.  But 
these  highest  expressions  of  social  living  have  their 
roots  in  tendencies  that  in  the  form  of  unconscious 
co-operation  accompany  animal  aggregations  extend- 
ing throughout  the  whole  animal  world,  as  well  as 
to  some  extent  among  plants.  Conceding  then  the 
difficulties  in  the  way  of  making  any  exact  definition 
of  social  behavior,  I  wish  to  present  some  of  the 
social  implications  of  mass  physiology,  particularly 
among  well-integrated  societies  of  animals. 

One  of  the  characteristics  of  social  life  among  the 
insects  is  the  presence  of  castes  (121)  which  perform 


SOCIAL   TRANSITIONS  25 1 

different  functions  within  the  colony.  With  many 
social  insects  the  division  of  labor  has  developed 
to  such  an  extent  that  the  animals  which  do  dif- 
ferent work  have  bodies  that  are  more  or  less  struc- 
turally appropriate  to  their  principal  tasks.  The 
reproductive  female  has  a  greatly  enlarged  ab- 
domen; the  soldier  grows  up  to  possess  large  jaws 
and  heavy  armor  or  other  protective  and  attacking 
devices;  a  worker  may  be  large  or  small  or  medium 
in  size,  according  as  its  size  will  best  suit  for  some 
of  the  varied  tasks  necessary  for  the  life  of  the  whole 
colony.  The  situation  is  greatly  different  from  that 
among  human  social  castes,  where  a  member  of  the 
aristocracy  may  be  as  husky  of  body  and  as  empty 
of  mind  as  the  most  menial  of  the  working  caste. 

The  only  physically  distinct  castes  to  be  found  in 
man  and  the  higher  vertebrates  are  those  associated 
with  sex.  In  sexual  forms  there  is  always  a  division 
of  labor  with  regard  to  the  primary  sexual  functions 
except  in  those  rare  cases,  usually  low  in  the  evo- 
lutionary scale,  which  at  one  and  the  same  time  are 
both  male  and  female.  With  many,  aside  from  pro- 
ducing eggs  rather  than  sperm,  it  is  difficult  to  find 
a  division  of  labor  or  of  appearance  between  the 
sexes.  With  others,  particularly  among  the  more 
specialized  animals,  there  are  differences  in  sexual 
behavior  and  responsibilities  which   are   associated 


252  THE  SOCIAL  LIFE  OF  ANIMALS 

with  the  more  fundamental  distinctions  of  sex.  Fre- 
quently, as  in  man,  these  differences  have  developed 
into  fairly  distinct  behavior  patterns  for  the  two 
sexes,  until  each  sex  is  practically  a  distinct  caste, 
almost  in  the  sense  used  in  discussing  castes  among 
the  social  insects. 

Sex  is  usually  determined  by  differences  in  he- 
redity which  are  associated  with  the  combination  of 
chromosomes  (37)  and  of  the  bearers  of  heredity 
(genes)  that  are  found  in  the  sperm  and  egg  whose 
union  gives  rise  to  the  new  individual.  Such  deter- 
minations occur  at  the  time  of  fertilization  and  sex 
is  normally  unaltered  thereafter. 

Exceptions  occur  which  demonstrate  that  for  cer- 
tain animals  this  normal  means  of  sex  determination 
can  be  overruled  by  environmental  differences.  Many 
of  these  cases  are  interesting  and  significant  but  their 
full  consideration  here  would  draw  us  off  the  main 
thread  of  our  present  discussion.  We  shall  follow 
only  those  instances  in  which  changes  in  sex  are 
associated  with  the  near-by  presence  of  other  indi- 
viduals, considering  here  two  widely  differing  cases 
which  have  been  carefully  investigated  in  recent 
years. 

Professor  Coe  (35)  of  Yale  has  spent  much  of  his 
time  studying  the  sex  ratios  and  sexual  changes  in 
oysters,  clams,  marine  snails  and  other  related  forms. 


SOCIAL    TRANSITIONS  253 

In  many  of  these  mollusks  he  has  found  that  the  sex 
ratios  vary  greatly  in  different  environments,  and 
has  reached  the  conclusion  that  frequently  among 
these  animals  the  expression  of  an  innate  sexual 
tendency  may  be  in  part  suppressed  or  stimulated, 
as  the  case  may  be,  by  the  environment  in  which 
any  given  animal  is  living. 

A  pertinent  case  is  that  of  a  set  of  marine  snails 
of  the  genus  Crepidula.  Three  of  these  "boat-shell" 
snails  are  common  animals  in  the  coastal  waters  of 
southern  New  England.  Their  sexual  history  follows 
similar  outlines.  After  a  juvenile  period  which  is 
essentially  asexual,  the  growing  Crepidula  becomes 
first  a  male  and  then  later,  sometimes  only  at  long 
last,  it  transforms  into  a  female.  A  typical  species  to 
follow  through  this  transformation  is  Crepidula  for- 
nicata. 

When  young,  these  animals  move  about,  but  as 
they  become  older  and  larger  they  settle  down  in 
one  place  on  a  wharf  piling  or  a  rock  or  another 
shell.  If  the  larger,  older  animals  are  broken  loose 
the  soft  parts  are  usually  destroyed  by  some  predator 
before  they  can  reattach  themselves,  leaving  behind 
the  relatively  heavy  shell.  Frequently  they  form 
large  chains  of  individuals,  of  which  a  simple  exam- 
ple is  shown  in  Figure  45.  The  large,  bottom  snail 


254  THE  SOCIAL  LIFE  OF  ANIMALS 

is  dead.  Attached  to  its  shell  is  a  large  female  which 
in  summer  actively  produces  eggs.  Above  her  are 
two  individuals  that  are  undergoing  transformation 
from  male  to  female.  Scattered  about  over  these  are 


Fig.  45.  Crepidula  fornicata.  (A)  A  basal  female  is 
attached  to  a  dead  shell  (D);  two  individuals  are  in  tran- 
sition stages  and  there  is  one  male  at  the  apex;  three 
motile  supplementary  males  are  in  mating  position  on 
the  lower  transition  individual.  (B)  same  group  from  the 
left  side.  (From  Coe.) 

four  smaller  snails  which  are  still  functional  males 
and  which  can  and  do  move  about.  Each  male  has 
a  long  slender  penis  by  means  of  which  he  transfers 
sperm  from  his  body  to  an  appropriate  receptacle 
in  the  body  of  the  female.  Several  males  may  par- 
ticipate in  the  insemination  of  a  single  female. 

The  growth  of  these  snails  is  fairly  rapid.  A  young 
snail  hatched  out  early  in  the  summer  may,  before 
autumn,  become  a  functional  male  about  16  mm. 
long,  which  is  about  two-fifths  the  size  of  a  fully 


SOCIAL   TRANSITIONS  255 

adult  female;  during  the  following  year  he  will 
probably  transform  into  a  female. 

The  relationships  which  Dr.  Coe  observed  at 
Woods  Hole  may  be  summarized  briefly.  Some  two 
hundred  young  males  were  taken  from  their  normal 
surroundings  and  placed  in  separate  containers  in 
the  laboratory.  Two  months  later  only  ii  per  cent 
were  still  functional  males;  15  per  cent  had  trans- 
formed completely  into  functional  females  and  the 
other  74  per  cent  were  on  their  way  in  that  direc- 
tion. Random  collections  of  snails  of  similar  sizes 
which  had  been  left  alone  in  their  natural  associa- 
tions showed  that  85  per  cent  were  still  functional 
males  and  only  3  per  cent  had  fully  changed  into 
females. 

Coe  summarizes  his  work  with  this  and  the  other 
Crepidulas  as  follows:  "There  is  no  doubt  but  that 
in  each  of  these  three  species  of  Crepidula  stable 
environmental  conditions  tend  to  prolong  the  male 
phase  of  these  individuals  that  are  suitably  mated 
and  sedentary."  These  points  are  further  illustrated 
in  his  diagram,  a  part  of  which  is  reproduced  in 
Figure  46. 

There  is  evidence  from  the  earlier  work  of  other 
observers,  (54,  87)  which  these  recent  studies  do  not 
entirely  replace,  that  association  with  a  female  is 
important  for  the  full  realization  of  the  male  con- 


2r.6 


THE  SOCIAL  LIFE  OF  ANIMALS 


dition  as  well  as  for  its  prolongation.  With  these 
snails  the  tendency  to  become  first  a  male  and  later 
a  female  is  probably  determined  by  heredity,  al- 
though the  hereditary  mechanism  which  promotes 
such  a  shift  is  at  present  unknown.  The  point  of 
interest   for   this   discussion   is   that  the   association 


CFORNICATA 


Fig.  46.  As  Crepidula  fornicata  gets  older  and  larger 
it  passes  successively  from  the  sexually  immature 
through  the  male  on  into  a  final  female  stage.  Mated 
males  retain  that  stage  longer  than  if  actively  motile. 
(From  Coe.) 

with  others,  especially  among  mated  males,  tends  to 
postpone  transformation  to  the  opposite  sex. 

Some  cases  are  known  in  which  the  presence  of 
other  animals  of  the  same  species  determines  the 
sex.  One  of  the  most  thoroughly  studied  is  that  of 
the  worm  Bonellia,  (21)  in  which  the  sexually  un- 
differentiated larva  does  not,  in  nature,  become  the 
small  parasitic  male  unless  it  is  associated  with  the 
large  female. 

Among  certain  nematode  worms  which  are  para- 
sitic in  insects,  if  few  eggs  are  introduced  into,  for 
example,    grasshoppers,    (3)    most    of    the    resulting 


SOCIAL   TRANSITIONS  257 

nematode  parasites  are  females;  but  if  many  eggs 
are  fed,  the  nematodes  that  hatch  are  almost  all 
males.  The  results  are  not  to  be  ascribed  to  a  differ- 
ential death  rate,  for  approximately  75  per  cent  of 
the  eggs  develop  in  both  cases. 

In  Crepidula  and  Bonellia  and  nematodes,  both 
males  and  females  are  always  present  in  a  popula- 
tion, though  in  differing  ratios.  In  cladocerans,  how- 
ever, of  which  Daphnia  is  an  example,  the  species 
may  be  carried  along  for  many  generations  by  the 
females  alone.  They  produce  eggs  which  do  not  re- 
quire fertilization,  but  which  develop  directly  into 
females  that  again  produce  other  females  like  them- 
selves. In  these  cladocerans  the  race  is  usually  made 
up  of  females  alone,  but  at  times  there  is  an  out- 
break of  sexuality;  males  and  sexual  females  appear 
and  the  fertilized  eggs  which  result  from  their  union 
are  more  resistant  to  adverse  conditions  than  those 
which  are  ordinarily  produced  and  which  require 
no  fertilization.  These  resistant  eggs  enable  the  spe- 
cies to  survive  times  of  environmental  stress,  such  as 
winter's  ice  or  the  drying-up  of  the  ponds  in  which 
these  small  crustaceans  live. 

In  one  species  of  Moina,  (5)  which  has  been 
much  studied  by  the  biologists  at  Brown  University, 
crowding  of  the  females  is  an  effective  method  of 
bringing  on  the  outbreak  of  males  and  sexual  fe- 


258  THE  SOCIAL  LIFE   OF  ANIMALS 

males,  so  that  overcrowding  may  be  rated  as  a  time 
of  environmental  stress.  Either  by  the  shortage  of 
food,  by  the  accumulation  of  waste  products,  or 
from  some  other  cause,  the  association  of  many  fe- 
male cladocerans  together  results  in  the  production 
of  eggs  which  have  a  different  prospective  potency 
from  those  the  same  females,  uncrowded,  would 
produce;  and  sexual  males  and  females  are  the  result. 

It  is  evident  from  these  varying  examples  that 
even  the  fundamental  matter  of  sex,  with  the  caste* 
like  divisions  of  labor  that  result  from  two  sexes, 
may  be  determined  by  the  close  association  of  ani- 
mals of  the  same  species.  There  is  some  reason, 
though  perhaps  it  is  slight,  for  suggesting  as  in 
Chapter  III  that  sex  itself  may  have  grown  origi- 
nally out  of  mutual  acceleration  in  division  rates 
when  two  or  more  primitive  organisms  were  in  close 
contact  in  small  space.  The  whole  matter  of  sex  may 
hark  back  to  some  of  the  basic  aspects  of  mass  physi- 
ology which  were  set  forth  earlier  in  this  book. 

Sex  in  its  different  aspects  plays  a  highly  impor- 
tant role  in  the  social  affairs  of  animals.  It  is  inter- 
esting to  find  that  this  fundamental  cleavage  through 
so  much  of  animal  life  can  at  times  be  controlled 
by  group  relationships.  Such  considerations  serve 
again  to  emphasize  the  difficulty  of  drawing  a  hard 


SOCIAL   TRANSITIONS  259 

and  fast  line,  or  even  a  fairly  distinct  band  between 
social  and  sub-social  living. 

One  phase  of  the  social  implications  of  sex  has 
escaped  general  comment.  I  heard  it  first  mentioned 
by  Professor  Wheeler.  (123)  Apparently  when  there 
is  a  social  difference  between  the  sexes  it  is  the  fe- 
males that  are  the  more  and  the  males  the  less  social; 
and  the  few  striking  exceptions  only  confirm  the 
rule. 

Among  the  social  ants,  bees  and  wasps  the  normal 
affairs  of  the  colony  are  carried  on  by  the  females. 
They  produce  males  only  when  they  are  needed  to 
fecundate  the  young  virgin  females  at  the  time  of 
their  nuptial  flight.  The  males  contribute  nothing 
to  the  protection,  feeding  or  housing  of  the  colony; 
after  their  one  sexual  activity  they  die  or  are  killed 
off,  and  the  females  which  are  lucky  enough  to 
secure  a  good  nesting  site  carry  on  with  their  female 
offspring  until  sexual  reproduction  again  becomes 
the  order  of  the  day  (Figure  47). 

With  many  of  the  herds  of  mammals,  the  main 
duties  of  communal  life  are  borne  by  the  females. 
They  protect  and  rear  the  young  and  herd  together 
to  protect  each  other.  The  males  keep  to  themselves 
except  during  the  relatively  brief  period  of  the 
sexual  rut.  Even  when  they  join  the  main  herds,  as 
in  the  case  of  the  Scottish  red  deer,  frequently  the 


26o  THE  SOCIAL   LIFE   OF  ANIMALS 

males  do  not  fuse  with  the  others.  When  danger  ap- 
pears during  the  rut,  the  stags  make  off  and  rejoin 
the  females  when  it  is  past.  After  a  male  is  sexually 
spent,  frequently  before  the  close  of  the  breeding 
season,  he  withdraws,  and  the  spent  males  form  stag 


Fig.  47.    Castes  of  the  common  honey-bee;  a,  queen;  b, 
male  (drone);  c,  worker.  (After  Phillips.) 

parties  which  are  distinctly  less  social  than  the  bands 
of  females. 

In  commenting  on  the  relative  sociability  of  the 
sexes  among  red  deer,  Darling  says:  (38)  "Matriarchy 
makes  for  gregariousness  and  family  cohesion.  The 
patriarchal  group  (among  deer)  can  never  be  large, 
for  however  attentively  the  male  may  care  for  his 
group  he  is  never  selfless.  Sexual  jealousy  is  always 
ready  to  impinge  on  social  relations  leading  to  gre- 
gariousness. ...  I  contend  that  the  matriarchal  sys- 
tem in  animal  life,  being  selfless,  is  a  move  toward 
the  development  of  an  ethical  system." 


SOCIAL   TRANSITIONS  26 1 

The  flocks  of  male  birds  whose  social  organization 
we  have  studied  in  Chapter  VI  are  more  combative 
than  the  females.  The  human  male  writes  the  great 
poems,  builds  the  great  bridges,  performs  the  out- 
standing scientific  research;  but  he  is  also  the  crim- 
inal, the  war-maker,  the  disturber  of  the  peace.  It 
is  the  human  female  that  is  the  highly  social  force 
with  our  species,  and  in  this  we  are  again  similar 
to  the  others  mentioned. 

Among  the  social  animals  only  the  termites  have 
fully  socialized  males;  with  them  the  male  reproduc- 
tives  consort  with  the  female  throughout  life.  Half 
the  soldiers  are  males  and  the  other  half  are  females, 
and  so  are  the  workers.  Termites  are  lowly  insects, 
but  in  this  one  trait  they  lead  the  world.  No  one 
knows  how  the  socialization  of  male  termites  was 
brought  about,  and  if  we  should  learn  their  secret 
it  probably  could  not  be  applied  directly  to  human 
affairs. 

When  we  turn  from  the  far-reaching  division  of 
most  animals  into  two  sexual  castes  to  explore  the 
origin  of  the  more  specialized  castes  of  insects,  we 
find  two  different  essential  kinds,  the  reproductives 
and  the  sterile  types.  With  bees,  ants  and  wasps,  for 
example,  the  usual  reproductive  females  can  pro- 
duce eggs  without  being  fertilized  by  a  sperma- 
tozoan.  Such  eggs  always  give  rise  to  males.  From 


262  THE  SOCIAL  LIFE  OF  ANIMALS 

the  Store  of  sperm  which  she  received  in  the  nuptial 
flight  the  same  female  can  allow  her  eggs  to  be  fer- 
tilized; such  fertilized  eggs  become  females. 

We  have  seen  the  comparative  unimportance  of 
the  males.  Although  the  active  colony  is  usually 
composed  of  females  only,  these  may  be  quite  dif- 
ferent in  appearance  and  function.  Typically  there 
are  the  reproductive  females  and  the  sterile  ones. 
Among  the  ants  the  sterile  females  are  divided  into 
the  protective  soldiers,  whose  main  function  is  to 
protect  the  colony  from  the  attack  of  other  species 
of  animals,  and  the  workers  proper.  The  ant  work- 
ers are  subdivided  on  the  basis  of  size  (Figure  48). 

Professor  Wheeler  made  the  study  of  these  social 
insects,  particularly  the  ants,  his  life  work.  In  a 
small  book,  published  in  1937  after  his  death,  he 
reaffirmed  his  belief  that  ants  and  bees  have  evolved 
from  ancestral  wasps,  and  that  each  has  developed 
the  caste  system  independently.  (124) 

With  bees  and  wasps,  whether  a  given  fertilized 
egg  is  to  produce  a  worker  or  a  sexual  "queen,"  bet- 
ter called  a  reproductive  female,  depends  on  the 
treatment  and  food  which  is  given  to  the  grub 
which  hatches  from  the  egg.  If  she  receives  plenty 
of  food  and  is  given  space  in  which  to  grow  she 
becomes  fully  matured  sexually;  if  fed  less  and  kept 
more   crowded   she   becomes   an   incomplete   female 


Fig.  48.  Some  ant  castes:  a,  soldier;  b,  form  interme- 
diate between  soldier  and  worker;  c,  worker;  d,  form  in- 
termediate between  soldier  and  worker;  e,  queen  that 
has  shed  her  wings;  i,  winged  mal^.  (After  Wheeler.) 


264  THE  SOCIAL   LIFE   OF  ANIMALS 

and  is  known  as  a  worker.  Apparently  the  funda- 
mental difference  can  be  brought  about  only  by  the 
treatment  which  the  developing  grub  receives  after 
hatching,  and  is  not  a  matter  of  heredity.  Just  how 
the  workers  are  stimulated  to  give  one  or  more  grubs 
the  treatment  that  will  allow  them  to  develop  their 
full  reproductive  capacities  is  not  fully  known.  If, 
however,  the  queen  bee  dies  or  is  removed  from  the 
colony,  workers  will  start  enlarging  one  or  more  of 
the  cells  which  contain  developing  grubs,  change 
their  care  and  feeding  and  so  allow  them  to  trans- 
form into  fertile  reproductives.  Perhaps  they  are 
kept  from  doing  so  when  a  queen  is  present  by  some- 
thing like  a  social  hormone,  which  there  is  good  rea- 
son for  thinking  is  produced  by  the  even  more  social 
termites. 

The  mechanism  which  results  in  caste  formation 
among  ants  need  not  be  the  same  as  that  in  wasps 
and  bees,  since  it  is  generally  conceded  that  they 
had  a  separate  social  evolution.  For  years  two  theo- 
ries have  been  promoted  as  to  how  ant  castes  came 
into  being.  One  group  of  students  thought  that  ant 
castes  were  determined  as  were  those  of  bees  and 
wasps,  by  care  and  food;  another  group  w^as  equally 
sure  that  the  differences  were  hereditary.  After  con- 
fessedly wavering  between  the  two  views  in  his  long 
study  of  ants.  Professor  Wheeler  in  his  posthumous 


SOCIAL   TRANSITIONS  265 

book  presents  the  evidence  which  finally  caused  him 
to  decide  that  with  ants  the  whole  matter  of  caste 
formation  is  primarily  controlled  by  heredity. 

This  is  a  question  which  will  undoubtedly  occupy 
students  of  ants  for  years  to  come.  The  evidence  is 
not  all  in,  and  the  fact  that  at  present  it  tends  to 
indicate  that  ant  castes  are  determined  by  heredity 
makes  all  the  more  interesting  the  instances  in  three 
separate  kinds  of  social  insects  of  the  apparent  evo- 
lution of  group  control  of  castes  after  the  hatching 
of  the  egg.  To  this  hasty  sketch  of  the  operation  of 
group  determination  of  caste  in  wasps  and  bees  may 
be  added  that  of  termites. 

The  bees  and  their  allies  belong  to  one  of  the 
most  specialized  of  insect  orders,  so  that  they  are 
assigned  a  high  position  in  the  evolutionary  tree  of 
that  class  of  animals.  The  termites,  miscalled  white 
ants,  belong  to  a  relatively  unspecialized  insect  order 
related  to  the  cockroaches,  and  stand  low  in  the 
evolutionary  scale  among  the  insects.  They  have, 
however,  reached  a  high  state  of  social  development. 

Unlike  bees,  ants  and  wasps,  the  colony,  as  we 
have  said,  is  at  all  times  composed  of  males  and  fe- 
males in  approximately  equal  numbers.  There  are 
male  and  female  reproductives.  of  which  three  dif- 
ferent kinds  are  known;  these  are  the  so-called  first 
form  which  have  wings  for  a  time  and  engage  in  a 


266  THE  SOCIAL  LIFE   OF  ANIMALS 

nuptial  flight,  second  form  reproductives  with  wing 
buds,  and  third  form,  which  are  wingless;  and  there 
are  the  sterile  workers  and  soldiers  in  which  both 
sexes  are  also  represented  equally.  The  colony  is 
usually  composed  of  reproductives  of  some  one  sort, 
and  the  two  sterile  castes  (Plate  V). 

The  controversy  as  to  whether  caste  formation  is 
a  result  of  heredity  or  of  the  social  environment  has 
been  as  intense  with  students  of  termites  as  among 
students  of  ants.  The  trend  of  present  information 
tends  to  support  the  theory  of  control  by  the  environ- 
ment. (27,  75)  A  certain  California  termite  called 
Zootermopsis  has  reproductives  and  soldiers  in  its 
colonies,  but  no  workers  in  the  accepted  sense  of  the 
term.  Their  place  is  taken  by  the  younger  nymphs, 
all  of  which  have  the  possibility  of  developing  into 
one  of  the  reproductive  grades  or  into  soldiers. 
When  Dr.  Castle  of  the  University  of  California  (27) 
set  up  experimental  colonies  of  nymphs  alone,  he  ob- 
tained in  due  time  one  or  more  pairs  of  reproduc- 
tives. If  the  small  experimental  colony  lacked  a  fer- 
tile male,  one  of  the  nymphs  developed  into  that;  if 
a  fertile  female  was  lacking  and  a  male  was  placed 
in  the  colony,  a  nymph  developed  into  a  fertile  fe- 
male. If  the  nymphs  in  a  colony  that  lacked  both 
males  and  females  were  fed  on  filter-paper  which 
contained  an  extract  of  fertile  females  made  with 


PLATE  V.  Winged  reprodiiciixe  caste,  soldiers  and 
workers  of  a  termite  from  British  Gtiiana.  This  is  one 
of  the  largest  species  of  termites  and  is  shown  life-size. 
A,  winged  reprodiictives;  B,  soldiers;  C,  workers.  (Pho- 
tograph by  AVilliam  Beebe.) 


SOCIAL    TRANSITIONS  267 

alcohol  or  ether,  the  males  appeared  at  the  usual 
time,  but  the  females  were  delayed  by  twelve  or  six- 
teen days  on  the  average. 

Ordinarily  in  Zootermopsis  only  one  soldier  ap- 
pears in  the  first  year  of  the  life  of  the  colony.  By 
removing  the  soldier  as  soon  as  it  appeared  in  the 
experimental  colony  it  was  possible  to  get  as  many 
as  six  soldiers  within  the  time  that  would  ordinarily 
have  yielded  only  one. 

In  explanation  of  these  and  other  similar  data 
Dr.  Castle  expresses  his  opinion  that  at  the  time  of 
hatching  all  nymphs  possess  three  sets  of  possibili- 
ties to  the  same  degree;  namely,  they  may  become 
sexually  mature  though  wingless,  they  may  become 
winged  and  sexually  mature,  or  they  may  become 
soldiers.  At  some  stage  these  chances  are  narrowed 
to  two  possibilities:  the  nymph  may  become  sexu- 
ally mature  or  it  may  develop  into  a  sterile  soldier. 
Since  the  reproductive  possibility  is  present  in  all 
nymphs  and  since  its  expression  is  inhibited  by  a 
substance  produced  by  a  functional  reproductive  and 
eaten  by  the  nymphs,  the  absence  of  functional  re- 
productives  would  allow  this  potential  power  to  ex- 
press itself.  Just  what  determines  that  one  of  the 
first  small  lot  of  eggs  will  become  a  soldier  is  not 
known,  but  it  can  easily  be  seen  that  when  one 
soldier  has  started  to  develop  it  too  may  give  off  an 


268  THE   SOCIAL   LIFE   OF  ANIMALS 

inhibiting  influence  which  prevents  other  nymphs 
from  becoming  soldiers.  In  the  normal  course  of 
events  a  second  soldier  appears  only  when  the  colony 
has  become  sufficiently  numerous  so  that  the  soldier- 
inhibiting  substance  is  spread  among  so  many  that 
the  effect  on  any  one  nymph  is  weakened;  and  some- 
thing of  the  same  effect  of  numbers  may  explain 
why,  in  a  large  colony,  many  nymphs  develop  at 
times  into  sexually  mature  and  winged  forms. 

There  seems  to  be  a  relation  to  the  more  gen- 
eralized situation  noted  earlier.  When  many  animals 
are  exposed  together  to  a  given  amount  of  alcohol 
or  some  other  toxic  material,  no  one  of  the  many 
may  receive  any  overdose,  as  will  certainly  happen 
when  one  or  a  few  individuals  meet  the  full  effect 
of  the  poison.  This  type  of  relatively  simple  mass 
effect,  first  discovered  in  experiments  on  group  phys- 
iology among  animals  that  at  the  most  are  only 
partially  socialized,  apparently  turns  out  to  be  an 
important  mechanism  in  regulating  caste  formation 
among  these  highly  social  termites;  and  some  simi- 
lar mechanism  may  control  the  activity  of  worker 
bees  in  producing  new  queens.  It  is  true  that  the 
control  of  caste  production  is  probably  not  the 
simplest  form  of  physiological  mass  action,  for  the 
insects  may  from  time  to  time  become  less  sensitive 
to   such   inhibition.    At   these   times,    many   of   the 


SOCIAL   TRANSITIONS  269 

nymphs  may  develop  into  the  winged  reproductives 
that  swarm  forth  in  the  nuptial  flight. 

As  many  know,  most  termites  eat  wood  which, 
paradoxically  enough,  they  are  unable  to  digest 
although  they  do  obtain  their  nourishment  from  it. 
The  answer  to  this  riddle  is  that  the  termites  harbor 
in  their  alimentary  canals  several  species  of  flagel- 
late protozoans  which  can  and  do  change  the  wood 
into  substances  which  both  termites  and  these  flagel- 
lates find  highly  nutritious. 

From  many  structural  relationships  we  know  that 
termites  are  close  relatives  of  cockroaches,  and  studies 
by  Dr.  Cleveland  of  Harvard  (34)  have  shown  how 
the  termite  societies  may  have  arisen  from  the  much 
less  social  cockroaches.  Here  we  have  an  example  of 
one  of  the  many  possible  connections  between  highly 
developed  social  life  and  the  less  social  state  illus- 
trated by  the  mass  physiology  characteristic  of  animal 
aggregations. 

Cryptocercus  is  a  wood-eating  cockroach  which  is 
found  in  decaying  wood  of  the  forests  of  the  Ap- 
palachian mountains  from  Pennsylvania  to  Georgia, 
and  along  the  coastal  mountains  in  the  northwestern 
part  of  the  United  States.  Like  their  relatives,  the 
termites,  these  cockroaches  feed  on  wood,  and  also 
like  the  termites  they  harbor  wood-digesting  pro- 
tozoans in  their  alimentary  tract.  These  wood  roaches 


2^0  THE  SOCIAL   LIFE   OF  ANIMALS 

and  many  termites  cannot  live  long  if  deprived  of 
their  associated  protozoa,  as  can  be  done  by  appropri- 
ate treatment  in  the  laboratory. 

The  young  of  both  cockroaches  and  termites  hatch 
out  without  these  essential  protozoans.  The  termites 
obtain  theirs  by  swallowing  a  drop  of  liquid  which 
has  just  emerged  from  the  anal  opening  of  another 
termite;  the  cockroaches  get  their  protozoans  by  eat- 
ing the  pellets  passed  from  the  alimentary  tract  of 
molting  individuals.  Once  a  cockroach  obtains  a 
good  supply  it  renews  itself.  One  such  cockroach 
or  a  pair  can  emigrate  to  a  new  log  and  live  there 
for  a  lifetime.  Since,  however,  adult  cockroaches  do 
not  molt,  the  young  of  such  an  isolated  pair,  when 
hatched,  could  not  receive  the  so-necessary  intestinal 
protozoa,  and  hence  a  pair,  if  isolated,  could  not 
found  a  new  colony.  Actually  the  eggs  hatch  at  just 
about  the  time  of  the  annual  molting  season  when 
the  young  growing  roaches  cast  their  outer  covering 
and  a  part  of  the  lining  of  their  alimentary  tract. 
At  this  time  the  newly  hatched  young  can  obtain 
protozoa  readily  and  thereafter  they  retain  them. 
The  habit  of  living  together  is  necessary  in  order 
that  the  growing,  molting  young  may  transmit  their 
protozoa  to  the  newly  hatched  nymphs. 

The  social  situation  is  still  more  necessary  for  the 
termites.  With  them  all  the  intestinal  protozoans  are 


SOCIAL    TRANSITIONS  27 1 

lost  with  each  molt,  and  each  time  that  happens 
each  newly  molted  individual  must  obtain  some  of 
the  protozoans  from  another  member  of  the  colony 
or  it  will  starve.  The  newly  hatched  termites  often 
obtain  protozoa  before  they  are  twenty-four  hours 
old,  and  an  artificially  defaunated  termite,  if  allowed 
to  associate  with  his  normal  fellows,  is  reinfected 
within  a  few  days.  With  the  termites,  colony  life  is 
an  absolute  essential  and  only  the  winged  males  and 
females,  the  first  form  reproductives  already  infected 
with  protozoans  before  taking  the  nuptial  flight,  can 
even  start  a  colony  without  the  presence  of  others  to 
carry  the  needed  cultures  of  protozoans. 

Many  cockroaches  which  neither  eat  wood  nor 
harbor  wood-digesting  protozoans  reproduce  so 
rapidly  that  given  good  hiding  places  and  plenty  of 
food  they  aggregate  in  large  numbers,  as  many 
housewives  know.  These  cockroach  aggregations, 
which  appear  to  be  formed  as  a  result  of  tropistic 
reactions  to  the  environment,  accompanied  by  tol- 
eration for  the  presence  of  others,  permitted  the 
wood-roach  Cryptocercus  to  develop  the  habit  of 
passing  protozoa  from  one  individual  to  another,  and 
so  began  the  long  evolution  which  has  resulted  in  the 
highly  adapted,  wood-eating  roaches  found  today. 

The  same  basic  adaptation  allowed  their  relatives, 
the  termites,  to  start  on  the  much  longer  road  they 


27^  THE  SOCIAL   LIFE   OF  ANIMALS 

have  traveled  to  reach  their  present  state  of  highly 
developed  social  life. 

We  cannot  outline  the  steps  taken  very  closely,  but 
it  would  seem  that  in  this  cockroach-termite  stock 
aggregations  allowed  aspects  of  mass  physiology  to 
develop  which  in  turn  permitted  a  closely  knit  and 
varied  social  evolution.  This  is  about  as  near  as  we 
have  yet  been  able  to  come  to  charting  a  direct  and 
obvious  truly  social  development  from  a  slightly  so- 
cial or  sub-social  animal  aggregation. 

Among  grasshoppers  crowding  can  produce  obvi- 
ous structural  changes  (Figure  49).  Certain  species  of 
grasshoppers  found  in  semi-arid  regions,  such  as 
those  of  South  Africa,  have  two  phases  (5)  that  are 
quite  distinct  from  each  other.  The  phases  are  suffi- 
ciently different  so  that  in  the  past  they  have  been 
described  as  being  different  species.  There  is  at 
present  much  evidence  which  indicates  that  the 
phase  solitaria  can  be  turned  into  phase  gregaria  by 
crowding  the  young  nymphs  into  dense  masses.  The 
opposite  transformation  may  take  place  when  the 
nymphs  of  phase  gregaria  are  reared  under  un- 
crowded  conditions.  The  differences  between  the  two 
extend  into  color,  form  and  size. 

Similarly  plant-lice,  which  are  also  called  aphids, 
exist  in  wdnged  and  wingless  forms  which  tend  to 
alternate.  When  the  wingless  aphids  have  approxi- 


1^. 


Fig.  49.  The  five  upper  nymphs  (1-5)  and  the  lowest 
adult  belong  to  the  swarm  phase;  the  others  (6-11)  show 
different  aspects  of  the  solitary  phase  of  the  brown 
locust  (Locustana  pardalina)  of  SoTith  Africa.  This  is  a 
black-and-white  copy  of  a  color  plate  by  Faure.  Black 
here  represents  black  or  bluish-black  in  the  grasshop- 
pers; heavy  stippling  represents  dark  brown;  light  stip- 
pling represents  light  or  golden-brown  except  in  parts 
of  Nos.  7  and  9  which  are  green. 


274  THE  SOCIAL  LIFE  OF  ANIMALS 

mately  exhausted  the  juices  from  one  food  plant  the 
next  generation  appears  with  wings;  in  flying  about, 
some  of  them  will  usually  find  a  new  and  suitable 
food  plant  where  they  can  settle  and  carry  on.  With 
some  species  one  of  the  most  effective  ways  of  keep- 
ing wings  from  developing  is  to  isolate  the  individ- 
ual aphids  and,  conversely,  one  of  the  best  recipes 
for  obtaining  winged  forms  is  to  allow  them  to  be- 
come crowded.  (104) 

These  distinctly  different  types  of  grasshoppers 
and  aphids  roughly  suggest  the  structural  differences 
between  the  castes  of  social  insects,  just  as  compari- 
son was  suggested  between  the  structural  differences 
of  caste  and  of  sex.  The  resemblance  is  so  close  that 
the  line  cannot  be  drawn  between  its  manifestations 
in  social  and  infrasocial  animals.  Not  only  that,  but 
the  mechanisms  by  which  the  castes  are  produced 
appear  in  many  instances  to  be  like  those  which  may 
occur  when  animals  are  aggregated  together,  even 
though  the  aggregations  are  below  the  level  usually 
regarded  as  marking  the  lower  limit  of  truly  social 
life. 

And  since  no  one  has  yet  demonstrated  the  exist- 
ence of  truly  asocial  animals  it  is  impossible  to  define 
the  lower  limits  of  sub-social  living.  All  that  can  be 
found  is  a  gradual  development  of  social  attributes, 
suggesting,  as  has  been  emphasized  throughout  this 


SOCIAL   TRANSITIONS  275 

book,  a  substratum  of  social  tendencies  that  extends 
throughout  the  entire  animal  kingdom.  From  this 
substratum  social  life  rises  by  the  operation  of  dif- 
ferent mechanisms  and  with  various  forms  of  expres- 
sion until  it  reaches  its  present  climax  in  vertebrates 
and  insects.  Always  it  is  based  on  phases  of  mass 
physiology  and  social  biology  which  taken  alone  seem 
to  be  social  by  implication  only. 


Literature  Cited  * 


1.  Allee,  W.  C.  1912.  "An  experimental  analysis  of  the 
relation  between  physiological  states  and  rheo- 
taxis  in  Isopoda,"  /.  Exp.  Zool.  13:269-344. 

2. 1920.  "Animal  aggregations,"  Anat.  Rec.  17:340. 

3. 1931-  Animal  Aggregations,  a  Study  in  General 

Sociology,  Chicago:  University  of  Chicago  Press. 
431  pp. 

4. 1932.  Animal  Life  and  Social  Growth,  Baltimore: 

Williams  and  Wilkins.  159  pp. 

5. 1934.  "Recent  studies  in  mass  physiology,"  Biol. 

Rev.  9:1-48. 

6. 1936.  "Analytical  studies  of  group  behavior  in 

birds,"  Wilson  Bull.  48:145-51. 

7. 1937.  "Evolution  and  behavior  of  the  inverte- 
brates," in  The  World  and  Man  as  Science  Sees 
Them,  edited  by  F.  R.  Moulton.  Chicago:  Uni- 
versity of  Chicago  Press,  pp.  294-346. 

8.  Allee,  W.  C,  and  Bowen,  Edith.   1932.  "Studies  in 

animal  aggregations:  mass  protection  against  col- 
loidal silver  among  goldfishes,"  /.  Exp.  Zool. 
61:185-207. 

9.  Allee,  W.  C,  and  Collias,  N.  Unpublished  results. 
10.  Allee,  W.   C,  and  Evans,   Gertrude.    1937a.   "Some 

*  No  attempt  has  been  made  to  document  the  text  fully  or  to  cite 
all  of  the  important  books  and  papers  which  have  been  consulted 
intensively.  Many  of  these  are  cited  in  the  bibliographies  to  be 
found  in  the  items  here  listed. 

277 


278  LITERATURE   CITED 

effects  of  numbers  present  on  the  rate  of  cleavage 
and  early  development  in  Arhacia,"  Biol.  Bull. 
72:217-32.  1937b.  "Further  studies  on  the  effect  of 
numbers  on  the  rate  of  cleavage  in  eggs  of 
Arbacia/'  J.  Cell,  and  Comp.  Physiol.  10:15-28. 
1937c.  "Certain  effects  of  numbers  present  on  the 
early  development  of  the  purple  sea-urchin, 
Arbacia  punctulata:  a  study  in  experimental 
ecology,"  Ecology  18:337-45. 

11.  Allee,  W.  C,  and  Masure,  R.  H.  1936.  "A  compari- 

son of  maze  behavior  in  paired  and  isolated  shell- 
parrakeets  (Melopsittacus  undulatus  Shaw)  in  a 
two-alley  problem  box,"  /.  Comp.  Psych.  22:131- 

56. 

12.  Allee,  W.  C,  and  Wilder,  Janet.  1938.  "Group  pro- 

tection for  Euplanria  dorotocephala  from  ultra- 
violet radiation,"  Physiol.  Zool.  In  press. 

13.  Allee,  W.  C,  Bowen,  E.,  Welty,  J.,  and  Oesting,  R. 

1934.  "The  effect  of  homotypic  conditioning  of 
water  on  the  growth  of  fishes,  and  chemical  studies 
of  the  factors  involved,"  /.  Exp.  Zool.  68:183-213. 

14.  Allee,  W.  C,  Oesting,  R.,  and  Hoskins,  W.  1936.  "Is 

food  the  effective  growth-promoting  factor  in 
homotypically  conditioned  water?"  Physiol.  Zool. 

9:409-32. 

15.  Allport,    F.    H.    1924.    Social    Psychology,    Boston: 

Houghton  Mifflin.  453  pp. 

16.  Alverdes,  Friedrich.  1927.  Social  Life  in  the  Animal 

Worlds  New  York:  Harcourt  Brace.  216  pp. 

17.  Andrews,  R.  C.  1926.  On  the  Trail  of  Ancient  Man; 

a  narrative  of  the  field  work  of  the  Central  Asiatic 
expeditions.  New  York:  Putnam.  375  pp. 

18.  The  Auk,  in  Notes  and  Comments.  N.  S.  49:524. 

1932. 

19.  Bailey,  V.    1931.  Mammals  of  New  Mexico,  U.   S. 

Dept.  Agric.  Bur.  of  Biol.  Survey.  N.  Amer.  Fauna 
no.  53.  412  pp. 


LITERATURE    CITED  279 

20.  Baker,  O.  E.  1937.  "Human  resources  of  the  United 

States,"    Science;    Science    News    Supplement    86 

(2223):i2. 

21.  Baltzer,  F.  1928.  "Uber  metagame  Geschlechtsbestim- 

mung  und  ihre  Beziehung  zu  einigen  Problemen 
der  Entwicklungsmechanik  und  Vererbung" 
(Zusammenfass.  Schrift),  Verh.  d.  Deutsch.  Zool. 
Gesellsch.  32:273-325. 

22.  Bates,  H.  W.   1892.    The  Naturalist  on   the  River 

Amazons,  London:  Murray.  395  pp. 

23.  Bayer,    E.    1929.    "Beitrage    zur   Zweikomponenten- 

theorie  des  Hungers,"  Zeit.  f.  Psych.  112:1-54. 

24.  Beebe,  W.,  Hartley,  G.,  and  Howes,  P.  1916.  Tropi- 

cal Wild  Life  in  British  Guiana,  New  York:  New 
York  Zool.  Soc.  504  pp. 

25.  Blatz,  W.  C,  Millichamp,  D.,  and  Charles,  M.  1937. 

"The  early  social  development  of  the  Dionne 
quintuplets,"  University  of  Toronto  Studies. 
Child  Development  Series  No.  13.  40  pp.  Or  in 
Collected  Studies  on  the  Dionne  Quintuplets. 
University  of  Toronto  Press. 

26.  Bohn,  G.,  et  Drzewina,  A.   1920.  "Variations  de  la 

sensibilite  a  I'eau  douce  des  Convoluta  suivant  les 
^tats  physiologiques  et  le  nombre  des  animaux  en 
experience,"  C.  R.  Acad.  Sci.  171:1023-25. 

27.  Castle,  G.  B.  1934.  "An  experimental  investigation 

of  caste  differentiation  in  Zootermopsis  augusti- 
collis/'  in  Termites  and  Termite  Control,  edited 
by  C.  A.  Kofoid.  Berkeley:  University  of  Cali- 
fornia Press.  2nd  edition,  pp.  292-310. 

28.  Chapman,  F.  M.  1935.  "The  courtship  of  Gould's 

manakin  on  Barro  Colorado  Island,  Canal  Zone," 
Bull.  Amer.  Mus.  Nat.  Hist.  68:471-523. 

29.  Chen,    S.    C.    1938a.    "Social^  modification    of    the 

activity  of  ants  in  nest  building,"  Physiol.  Zool. 
10:420-36.  1938b.  "The  leaders  and  followers 
among  the  ants  in  nest  building,"  Ibid.  10:437-55. 


28o  LITERATURE  CITED 

30.  Chevillard,   L.    1935.    "Contribution    a   I'etude   des 

echanges  respiratoires  de  la  Souris  blanche  adult." 
II.  "La  temperature  corporelle  de  la  Souris  et  ses 
variations,"  Ann.  Physiol,  et  Physicochimie 
11:468-84. 

31.  Child,  C.  M.  1915.  Senescence  and  Rejuvenescence, 

Chicago:  University  of  Chicago  Press.  481  pp. 

32. 1924.    Physiological    Foundations    of    Behavior, 

New  York:  Holt.  330  pp. 

33.  Churchman,   J.,   and   Kahn,    Morton.    1921.    "Com- 

munal activity  of  bacteria,"  /.  Exp.  Med.  33:583- 

91- 

34.  Cleveland,  L.   R.    1934.   "The  wood-feeding  roach, 

Cryptocercus,  and  its  Protozoa,  and  the  symbiosis 
between  Protozoa  and  roach,"  Mem.  Amer.  Acad. 
Arts  and  Sci.  17:187-342. 

35.  Coe,  W.  R.  1936.  "Sexual  phases  in  Crepidula,"  J. 

Exp.  Zool.  72:455-77. 

36.  Crew,  F.  A.,  and  Mirskaia,  L.  1931.  "The  effects  of 

density  on  an  adult  mouse  population,"  Biol. 
Gen.  7:239-50. 

37.  Dansforth,  C.  H.  1934.  "The  interrelation  of  genetic 

and  endocrine  factors  in  sex,"  in  Sex  and  Internal 
Secretions,  edited  by  E.  Allen.  Baltimore:  Wil- 
liams and  Wilkins.  pp.  12-54. 

38.  Darling,  E.  Eraser.  1937.  A  Herd  of  Red  Deer,  Lon- 

don: Oxford  University  Press.  215  pp. 
39. 1938.  Bird  Flocks  and  the  Breeding  Cycle,  Lon- 
don: Cambridge  University  Press.  124  pp. 

40.  Deegener,  P.  1918.  Die  Formen  der  Vergesellschaft- 

ung  im  Tierreiche.  Ein  systematisch-soziologischer 
Versuch,  Leipzig:  Veit.  420  pp. 

41.  Dobzhansky,  T.   1937.   Genetics  and  the   Origin  of 

Species,  New  York:  Columbia  University  Press. 
364  pp. 

42.  Durkheim,  E.  1902.  De  la  divison  du  travail  social, 

Paris:  Alcan.  460  pp. 


LITERATURE    CITED  28 1 

43.  Ellis,  Havelock.   1929.   The  Dance  of  Life,  Boston: 

Houghton  Mifflin.  342  pp. 

44.  Espinas,  A.  V.    1878.   Des  societes  animales,  Paris: 

Bailliere.  582  pp. 

45.  Falk,  Isadore.  1927.  "Does  infant  welfare  operate  to 

preserve  the  unfit?"  Amer.  J.  Pub.  Health  17:142- 

47- 

46.  Fischel,    W.     1927.    "Beitrage    zur    Soziologie    des 

Haushuhns,"  BioL  Zentralhl.  47:678-96. 

47.  Folks,  Homer.  1920.  The  Human  Costs  of  the  War, 

New  York:  Harper.  326  pp. 

48.  Forbes,  S.  A.  1887.  "The  lake  as  a  microcosm,"  Bull. 

Peoria  Acad.  Sci.  Reprinted  in  ///.  State  Nat.  Hist. 
Survey  Bull.  15:537-50. 

49.  Forbush,   E.   H.    1925-1929.  Birds   of  Massachusetts 

and  Other  New  England  States,  Mass.  Dept.  Agric. 
Vols.  I-III. 

50.  Fowler,  J.  R.  1931.  "The  relation  of  numbers  of  ani- 

mals to  survival  in  toxic  concentrates  of  electro- 
lytes," Physiol.  Zool.  4:214-45. 

51.  Garner,  M.  R.  1934.  "The  relation  of  numbers  of 

Paramecium  caudatum  to  their  ability  to  with- 
stand high  temperatures,"  Physiol.  Zool.  7:408-34. 

52.  Gates,  Mary,  and  Allee,  W.  C.   1933.  "Conditioned 

behavior  of  isolated  and  grouped  cockroaches  on 
a  simple  maze,"  /.  Comp.  Psych.  15:331-58. 

53.  Gause,  G.  F.  1934.  The  Struggle  for  Existence,  Balti- 

more: Williams  and  Wilkins.  163  pp. 

54.  Gould,  H.  N.  1917a.  Studies  on  sex  in  the  hermaph- 

rodite mollusc  Crepidula  plana.  I.  "History  of  the 
sexual  cycle,"  /.  Exp.  Zool.  23:1-69.  1917b.  II.  "In- 
fluence of  environment  on  sex,"  Ibid.  23:225-50. 
1919.  III.  "Transference  of  the  male-producing 
stimulus  through  sea-water/'  Ibid.  29:113-20. 

55.  Grave,    B.    H.,    and   Downing,    R.    C.    1928.    "The 

longevity  and  swimming  ability  of  spermatozoa," 
/.  Exp.  Zool.  51:383-88. 


282  LITERATURE  CITED 

56.  Gross,  A.  O.  1928.  "The  Heath  Hen,"  Mem.  Bost. 

Soc.  Nat.  Hist.  6:491-588. 

57.  Gulick,  A.  1905.  "Evolution,  racial  and  habitudinal," 

Pub.  Carnegie  Inst.  25:1-269. 

58.  Hankins,  Frank  H.  1937.  "German  policies  for  in- 

creasing births,"  Amer.  J.  Soc.  42:630-52. 

59.  Harlow,  H.  F.  1932.  "Social  facilitation  of  feeding  in 

the  albino  rat,"  /.  Genet.  Psych.  41:211-21. 

60.  Harnly,  M.  H.  1929.  "An  experimental  study  of  en- 

vironmental factors  in  selection  and  population," 
/.  Exp.  Zool.  53:141-70. 

61.  Hicks,  Frederick.  1920.  The  New  World  Order,  New 

York:  Doubleday  Page.  496  pp. 

62.  Hogg,  Jabez.   1854.   "Observations  on  the  develop- 

ment and  growth  of  the  water  snail  (Lymnaeus 
stagnalis),"  Quart.  J.  Micros.  Sci.  2,  in  Trans. 
Micros.  Soc.  2:91-103. 

63.  Holmes,  S.  J.  1921.  The  Trend  of  the  Race;  a  study 

of  present  tendencies  in  the  biological  develop- 
ment of  civilized  mankind.  New  York:  Harcourt 
Brace.  396  pp. 

64. 1936.  Human   Genetics  and  Its  Social  Import, 

New  York:  McGraw-Hill.  414  pp. 

65.  Howard,  H.  E.  1920.  Territory  in  Bird  Life,  London: 

Murray.  308  pp. 

66.  Hudelson,  E.  1928.  Class  Size  at  the  College  Level, 

Minneapolis:  University  of  Minnesota  Press.  299 
pp.  1932.  "Class  size  at  the  college  level,"  No. 
Cent.  Assoc.  Quart.  6:371-81. 

67.  Hunt,  H.  R.  1930.  Some  Biological  Aspects  of  War, 

New  York:  Gal  ton.  118  pp. 

68.  Johnson,  W.  H.  1937.  "Experimental  populations  of 

microscopic  organisms,"  Amer.  Nat.  71:5-20. 

69.  Jones,  F.  M.  1931.  "The  gregarious  sleeping  habits 

of  Heliconius  charithonia  L."  Proc.  Ent.  Soc. 
London  6:4-10. 


LITERATURE    CITED  283 

70.  Jordan,  David  Starr.  1903.  The  Blood  of  the  Nation; 

a  study  of  the  decay  of  races  through  the  survival 
of  the  unfit,  Boston:  Amer.  Unitar.  Assoc.  82  pp. 
1907.  The  Human  Harvest;  a  study  of  the  decay 
of  nations  through  the  survival  of  the  unfit, 
Boston:  Amer.  Unitar.  Assoc.  122  pp.  1915.  War 
a7id  the  Breed;  the  relation  of  war  to  the  down- 
fall of  nations,  Boston:  Beacon  Press.  265  pp. 

71.  Jordan,  D.  S.,  and  Jordan,  H.  E.  1914.  War's  After- 

math, Boston:  Houghton  Mifflin.  103  pp. 

72.  Katz,   D.,    and   Toll,   A.    1923.    "Die   Messung  von 

Charakter-  und  Begabungs-unterschieden  bei 
Tieren  (Versuch  mit  Huhnern),"  Zeit.  f.  Psych. 
93:287-311. 

73.  Kellogg,  Vernon  L.  1912.  Beyond  War;  a  chapter  in 

the  natural  history  of  man.  New  York:  Holt. 
172  pp. 

74.  Kropotkin,  P.  1914.  Mutual  Aid,  a  Factor  in  Evolu- 

tion, 2nd  edition.  New  York:  Knopf.  223  pp. 

75.  Light,  S.  F.,  Hartman,  O.,  and  Emerson,  O,  H.  1938. 

"Social  hormones  in  the  termite  colony,"  Unpub- 
lished. 

76.  Livengood,  W.  1937.  "An  experimental  analysis  of 

certain  factors  affecting  growth  of  goldfishes  in 
homotypically  conditioned  water,"  Copeia  2:81-88. 

77.  Maclagen,  D.   S.    1932.    "The  effect   of  population 

density  upon  rate  of  reproduction  with  special 
reference  to  insects,"  Proc.  Roy.  Soc.  B  111:437-54. 

78.  Malinowski,  B.  1937.  "Culture  as  a  determinant  of 

behavior,"  in  Harvard  tercentenary  conference. 
Factors  Determining  Human  Behavior,  Cam- 
bridge: Harvard  University  Press.  168  pp. 

79.  Mast,  S.  O.,  and  Pace,  D.  1937.  "The  relation  be- 

tween the  number  of  individuals  per  volume  of 
culture  solution  and  rate  of  growth  in  Chilomonas 
Paramecium/'  Anat.  Rec.  70,  suppl.  40.  1938. 

80.  Masure,  R.  H.,  and  Allee,  W.  C.  1934.  "The  social 


284  LITERATURE  CITED 

order  in  flocks  o£  the  common  chicken  and  the 
pigeon,"  Auk  51:306-27. 

81.  Matthews,   L.    H.    1932.    "Lobster-krills;    anomuran 

Crustacea  that  are  the  food  of  whales,"  Discovery 
Reports,  Gov,  Dependencies,  Falkland  Islands 
5:467-84. 

82.  Mobius,  K.  1883.  "The  oyster  and  oyster  culture," 

U.  S.  Comm.  Fish  and  Fisheries.  Kept.  1880.  Part 
VIII:  683-751. 

83.  Murchison,   C.    1935a.   The   experimental   measure- 

ment of  a  social  hierarchy  in  Gallus  domesticus: 
I.  "The  direct  identification  and  direct  measure- 
ment of  social  reflex  No.  1  and  social  reflex  No. 
2,"  /.  Gen.  Psych.  12:3-39.  1935b.  II.  "The  identi- 
fication and  inferential  measurement  of  social  re- 
flex No.  1  and  social  reflex  No.  2  by  means  of  so- 
cial discrimination,"  /.  Soc.  Psych.  6:3-30.  1935c. 
III.  "The  direct  and  inferential  measurement  of 
social  reflex  No.  3,"  /.  Genet.  Psych.  46:76-102. 
i935d.  IV.  "Loss  of  body  weight  under  conditions 
of  mild  starvation  as  a  function  of  social  domi- 
nance," /.  Gen.  Psych.  12:296-312.  i935e.  V.  "The 
post-mortem  measurement  of  anatomical  fea- 
tures," /.  Soc.  Psych.  6:172-81. 

84.  Murphy,   G.,   and   Murphy,  L.    1931.  Experimental 

Social  Psychology,  New  York:  Harper.  709  pp. 

85.  Nichols,  J.  T.  1931.  "Notes  on  the  flocking  of  shore 

birds,"  Auk  48:181-85. 

86.  Oesting,  R.,  and  Allee,  W.  C.  1935.  "Further  analysis 

of  the  protective  value  of  biologically  conditioned 
fresh  water  for  the  marine  turbellarian,  Procer- 
odes  wheatlandi,  IV.  The  effect  of  calcium,"  Biol. 
Bull.  68:314-26. 

87.  Orton,  J.  H.  1909.  "On  the  occurrence  of  protandric 

hermaphroditism  in  the  mollusc  Crepidula  for- 
nicata,"  Proc.  Roy.  Soc.  London  81  6:468-84. 

88.  Park,  T.   1932.   "Studies  in  population  physiology: 


LITERATURE    CITED  285 

the  relation  of  numbers  to  initial  population 
growth  in  the  flour  beetle,  Triholium  confusum 
Duval,"  Ecology  13:172-82. 

89. 1933-    "Studies    in    population    physiology:    II. 

Factors  regulating  initial  growth  of  Tribolium 
confusum  populations,"  /.  Exp.  Zool.  65:17-42. 

90.  Patten,  William.  1920.  The  Grand  Strategy  of  Evolu- 

tion, Boston:  Gorham.  429  pp. 

91.  Peebles,    Florence.     1929.    "Growth-regulating    sub- 

stances in  Echinoderm  larvae,"  Biol.  Bull.  57:176- 

87. 

92.  Pearl,  Raymond.   1920.  "The  effect  of  war  on  the 

chief    factors    of    population    change,"     Science 

51-553-56. 

93. 1921.  "A  further  note  on  war  and  population," 

Science  53:120-21. 

94.  —  1936.    "War    and    overpopulation,"    Cur.    Hist. 

43:589-94- 

95.  Pearl,  R.,  and  Gould,  Sophia.  1936.  "World  popula- 

tion growth,"  Human  Biol.  8:399-419. 

96.  Pearl,  R.,  and  Parker,  S.  1922.  "On  the  influence  of 

density  of  population  upon  the  rate  of  reproduc- 
tion in  Drosophila/'  Proc.  Nat.  Acad.  Sci.  8:212-19. 

97.  Pearl,  R.,  Miner,  J.,  and  Parker,  S.   1927.  "Experi- 

mental studies  on  the  duration  of  life.  XI.  Density 
of  population  and  life  duration  in  Drosophila,'* 
Amer.  Nat.  61:289-318. 

98.  Phillips,  J.  Personal  communication. 

99.  Popenoe,  P.  B.,  and  Johnson,  R.  1918.  Applied  Eu- 

genics, New  York:  Macmillan.  429  pp. 

100.  Rabaud,  Etienne.  1937.  Phenomene  social  et  societes 

animates,  Paris:  Alcan.  321  pp. 

101.  Reich,  K.  Personal  communication. 

102.  Reighard,  J.  1893.  "The  ripe  eggs  and  spermatozoa 

of  the  wall-eyed  pike,"  Bien.  Rept.  Mich.  State 
Board  Fish  Comm.  10:93-171. 

103.  —  1920.   "The  breeding  behavior  of  the  suckers 


286  LITERATURE  CITED 

and  minnows.  I.  The  suckers,"  Biol.  Bull.  38:1-32. 

104.  Reinhard,  H.  J.  1927.  "The  influence  of  parentage, 

nutrition,  temperature  and  crowding  on  wing 
production  in  Aphis  gossypii,"  Texas  Agric.  Exp. 
Sta.  Bull.  353:5-19. 

105.  Retzlaff,  E.  Personal  communication. 

106. 1938.   "Studies  in  population  physiology  with 

the  albino  mouse,"  Biol.  Gen.  14:  (In  press) 

107.  Robertson,  T.  B.   1921.  "Experimental  studies  on 

cellular  multiplication.  II.  The  influence  of 
mutual  contiguity  upon  reproductive  rate  and 
the  part  played  therein  by  the  *X-substance'  in 
bacterised  infusions  which  stimulate  the  multi- 
plication of  Infusoria,"  Biochem.  J.  15:612-19. 

108.  Schjelderup-Ebbe,   T.    1922.    "Beitrage   zur   Sozial- 

psychologie  des  Haushuhns,"  Zeit.  f.  Psych. 
88:225-52. 

109 1931-    "E)ie    Despotic    im    sozialen    Leben    der 

Vogel,"  Thurnwald,  Forschungen  zur  Volker- 
psychologie  und  Sozialogie  10  (2):  77-140. 

110. 1935-  "Social  behavior  of  birds,"  in  A  Hand- 
book of  Social  Psychology,  edited  by  C.  Murchi- 
son,  pp.  947-72.  Worcester,  Mass:  Clark  Univer- 
sity Press. 

111.  Selous,  E.    1931.   Thought-transference  (or  What?) 

in  Birds,  New  York:  Smith.  255  pp. 

112.  Shaw,  Gretchen.   1932.  "The  effect  of  biologically- 

conditioned  water  upon  rate  of  growth  in  fishes 
and  Amphibia,"  Ecology  13:263-78. 

113.  Shoemaker,  H.  Personal  communication. 

114.  The   Statesman's   Year  Book.    1922-1936.   London: 

Macmillan. 

115.  Szymanski,  J.  S.  1912.  "Modification  of  the  innate 

behavior  of  cockroaches,"  /.  An.  Behav.  2:81-90. 

116.  Uvarov,    B.    P.    1928.    Locusts    and    Grasshoppers, 

London:  Imp.  Bur.  Entom.  352  pp. 

117.  Vetulani,    T.    1931.    "Untersuchungen    iiber    das 


LITERATURE    CITED  287 

Wachstum  der  Saugetiere  in  Abhangigkeit  von 
der  Anzahl  zusammengehaltener  Tiere.  I.  Teil 
Beobachtungen  an  Mausen,"  Biol.  Gen.  7:71-98. 

118.  Welty,  J.  C.  1934.  "Experiments  in  group  behavior 

of  fishes,"  Physiol.  Zool.  7:85-128. 

119.  Wheeler,  W.  M.  1913.  Ants,  their  Structure,  Devel- 

opment and  Behavior,  New  York:  Columbia 
University  Press.  663  pp. 

120. 1923.   Social  Life  among  the  Insects;  being  a 

series  of  lectures  delivered  at  the  Lowell  Insti- 
tute   in    Boston,    New    York:    Harcourt    Brace. 

375  PP- 

121. 1928.  The  Social  Insects,  their  Origin  and  Evolu- 
tion, New  York:  Harcourt  Brace.  378  pp. 

122. 1930-  "Societal  evolution,"  in  Human  Biology 

and  Racial  Welfare,  edited  by  E.  Cowdry,  pp. 
139-55.  New  York:  Hoeber. 

123. 1933-  Address  before  American  Society  of  Nat- 
uralists, Cambridge,  1933. 

124. 1937-   Mosaics   and    Other  Anomalies   Among 

Ants,  Cambridge:  Harvard  University  Press.  95 
pp. 

125.  Whelpton,  P.  K.  1935.  "Why  the  large  rise  in  the 

German  birth  rate?"  Amer.  J.  Soc.  41:299-313. 

126.  Wolfson,   C.    1935.   "Observations   on  Paramecium 

during  exposure  to  sub-zero  temperatures," 
Ecology,   16:630-39. 

127.  Wright,  S.  1931.  "Evolution  in  mendelian  popula- 

tions," Genetics  16:97-159.  1932.  "Roles  of  muta- 
tion, inbreeding,  crossbreeding  and  selection  in 
evolution,"  Proc.  6th.  Int.  Congress  Genetics 
1:356-66. 

128.  Zeller,  Eduard.   1931.   Outlines  of  the  History  of 

Greek  Philosophy,  New  York:  Harcourt,  Brace. 
324  pp. 

129.  Society  for  the  Psychological  Study  of  Social  Issues. 

1937.  Bulletin  2:11-12. 


Index 


^ 


Aggregations,  in  nature,  32; 
hibernating,  32;  breeding, 
33;  migrating,  33,  35,  37; 
various  examples,  34;  co- 
lonial animals,  41;  forced, 
42;  feeding,  44;  overnight, 
46,  248;  relation  to  social 
life,  49,  272 

Alcohol,  mass  protection  from, 

52 
Alverdes,  F.,  29 
Ancestral  tree  of  animals,  86, 

87 

Antelopes,  37 

Ants,  26,  32;  effect  of  num- 
bers on  digging,  139;  im- 
portance of  females,  259; 
castes,  262,  265 

Aphids,  272 

Appetite,  social,  44,  47,  247 

Arhacia  eggs,  69;  spermatozoa, 
69,  83;  effect  of  numbers  on 
rate  of  cleavage,  71;  effect 
of  extracts,  74 

Bacteria,  mass  protection,  67; 

food  for  protozoa,  77 
Baker,  O.  E.,  217 
Bats,  36 
Bavaria,     population     trend, 

223 
Beebe,  William,  248 


Bees,  26,  260,  262,  264,  265; 
solitary,  46;  importance, 
259;  castes,  260 

Beetles,  hibernation,  32 

Behavior,  of  isopods,  20; 
group,  §2,  133;  social  cri- 
teria of,  173 

Belgium,  population,  226,  227 

Bennet,  Mary,  185 

Birds,  33,  46,  47,  48,  88,  110, 
134'  155'  175'  206,  250,  261 

Birthrate,  219 

Bison,  38 

Bonellia,  256 

Bowen,  Edith,  92 

Breeding  season,  33,  133 

Butterflies,  overnight  aggrega- 
tions, 46 

Calcium,  protective  value,  65 
Canaries,    social    order,    191, 

193,  207 
Caribou,  37 
Caste,  250,  274 
Castle,  G.  B.,  266,  267 
Chapman,  Frank  M.,   134 
Chapman,  R.  N.,  104 
Chen,  S.  C,  139 
Chickens,   group   stimulation, 

135;  social  order,   176,   190, 

193,  207;  IQ,  192 
Child,  C.  M.,  58,  248 


290 


INDEX 


Children,  effect  of  class  size, 
143;  in  wartime,  230 

China,  population,  226;  racial 
vigor,  232 

Cladocera,  sex  determination, 

257 
Class   size,   effect   on   rate   of 

learning,  142 

Cleveland,  L.  R.,  269 

Cockroaches,  effect  of  num- 
bers on  rate  of  learning, 
149;  related  to  termites, 
265,  269 

Coe,  W.  R.,  252 

Collias,  N.,  185 

Colloidal  silver,  mass  protec- 
tion from,  53,  56 

Colonial  organisms,  41 

Community,  ecological,  38 

Confusion  effect,  139 

Conditioned  water,  64,  92 

Co-operation,  history,  23,  31; 
ecological,  40;  voluntary, 
42;  evidence  for,  49,  50;  un- 
conscious, 88,  133;  con- 
scious, 209;  principle  of, 
209,  211,  242,  243 

Copepods,  35 

Crepidula,  253 

Crowding,  harmful  effects,  31, 

50 
Ctenophores,  35 
Czechoslovakia,       population, 

227 
Cyprinodon,  learning,  164 

Daphnia,  mass  protection,  57, 
139;  food  for  fish,  137;  sex 
determination,  257 

Darling,  E.  Fraser,  111,  260 


Deegener,  P.,  28 
Deer,  48,  248,  259,  260 
Despotism,  185,  208 
Dionne  quintuplets,  201,  207 
Disease  in  wartime,  224,  225, 

228,  230,  231 
Division  of  labor,  32,  247,  251 
Dominance,  qualities  causing, 

190;    relation    to    breeding 

cycle,  194 
Drosophila,  effect  of  numbers 

on    rate    of    reproduction, 

103 

Eggs,  sea-urchin,  69 

Elephants,  minimal  popula- 
tion, 108 

Ellis,  Havelock,  24 

Emigration,  122,  126,  131 

Empedocles,  23 

England,  population  trend, 
219,  223,  226,  227 

Espinas,  A.  V.,  25,  28 

Euglena,  34 

Evans,  Gertrude,  73,  92 

Evolution,  course  of,  86,  87; 
effect  of  numbers  on  rate 
of,  118;  Lamar ckian,  118 

Family,  as  origin  of  society, 
47,  244,  248 

Finkel,  Asher,  92 

Fish,  schools,  48;  mass  pro- 
tection, 53,  56,  68;  effect  of 
crowding  on  growth,  92;  on 
amount  of  food  taken,  136; 
on  learning,  158;  leader- 
ship, 166;  imitation,  170 

Fischel,  W.,  196 


INDEX 


291 


Flocks  of  birds,  breeding,  111; 
social  organization,  175, 
206;  leadership  in,  196; 
wheeling  flight,  198;  of 
mixed  species,  197,  248 

Folks,  Homer,  230 

Forced  movements,  43.  (See 
Tropism) 

France,  population  trend,  223 

Fresh  water,  mass  protection 
from,  63 

Fundulus,  learning,   164 

Gates,  Mary,  149 

Gene  frequency,   118 

Germany,  population  trend, 
220,  223,  225,  226;  children 
in  wartime,  230 

Goldfish,  mass  protection,  53, 
56,  68;  effect  of  numbers  on 
growth  rate,  92;  on  amount 
of  food  taken,  136;  on 
learning,  159;  leadership, 
166;   imitation,    170 

Gross,  A.  O.,   113 

Group  behavior,  22,  133; 
stimulation  of  feeding,  136; 
organization,  175 

Growth,  retarded  by  over- 
crowding, 91;  of  goldfish, 
effect  of  numbers,  92;  ef- 
fect of  extracts  on,  72,  96; 
of  mice,  effect  of  numbers, 

99 
Gulls,     minimal     population, 
110;   effect  of  numbers  on 
survival,  111 

Hawaii,  snails,  123 
Heath  hen,  113,  122 


Henry  IV  of  France,  236 
Hibernation,  32,  58 
Holmes,  S.  J.,  231 
Hormones,    effect    on    social 
rank,    193;   social,   264,   267 
Hoskins,  Walter,  92 
Hunt,  Harrison,  228 

Imitation,  170 

Insects,  social,  26,  29,  32,  259; 

population    in    nature,    39; 

evolution  of,  88;  as  enemies 

of  man,  241;  castes,  250 
Instinct,  249;  definition,  246; 

social,  244,  245,  249 
International  relations,  210 
Isopods,  behavior,  20 
Italy,   population   trend,   219, 

225,   226,   227;   children  in 

wartime,  230 

Japan,  population,  226 
Johnson,  W.  H.,  77 
Jordan,  David  Starr,  228 

Kellogg,  John,  185 
Kessler,  K.  F.,  26 
Kropotkin,  Prince,  27 

Leader,  of  a  group,  166,  175, 
196,  207;  relation  to  peck- 
order,   199 

League  of  Nations,  236 

Learning,  effect  of  numbers, 
142 

Liven  good,  Wayne,  92 

Lobster-krills,  34 

Locusts,  migratory,  35;  phases, 
272 


292 


INDEX 


Malinowski,  B,,  213,  243 
Man,  26;  mass  protection,  52, 
85,  209;  evolution  of,  88; 
effects  of  numbers  on  men- 
tal work,  142;  social  rank- 
ing, 201;  war,  210;  enemies 
of,  240;  castes,  251;  com- 
bativeness,  261 
Manakin,  breeding  behavior, 

134 
Mass  protection,  52,  85 
Mast,  S.  O.,  81 
Masure,  R.,   185,   192 
May-flies,  35 
Maze  learning,    150;   relation 

to  social  rank,  192 
Metaphysics,  18 
Mice,    effect   of   numbers   on 

rate  of  growth,  99;  on  rate 

of  reproduction,  103 
Migration,  33 
Minnesota,     experiments     on 

class  size,  145 
Mixed    flocks,    leadership    in, 

48,  197 
Moina,     sex     determination, 

257 
Murchison,  C,  182 

Mutation,  118 

Newman,  H.  H.,  206 
Netherlands,  population,  226, 

227 
Nichols,  J.  T.,   197 


Paramecium,  76 
Park,  Thomas,  105 
Parrakeet,   effect  of   numbers 

present    on    learning,    155; 

social  order,  185,  191,  192 
Patten,  W.,  27 
Pearl,     Raymond,     107,     216, 

218,  222,  223,  224 
Peck-order,    176;    relation    to 

leadership,   199 
Phases  of  grasshoppers,  272 
Phillips,  John,  107 
Philosophy,   17,  23 
Pigeons,  social  order,  186,  207 
Planaria,  mass  protection,  59 
Poisons,  mass  protection  from, 

53'  56 

Poland,  children  in  wartime, 
230 

Popenoe  and  Johnson,  234 

Population,  optimal  size,  92, 
103,  104,  125,  128,  130,  131; 
minimal,  108;  human,  re- 
lation to  war,  214;  of  the 
world,  215,  218;  of  U.  S.  A., 
217;  of  various  countries, 
226 

Procerodes,    mass    protection, 

63 

Protozoa,  effect  of  numbers 
on  rate  of  division,  76;  ex- 
planation of  effect,  80;  as- 
sociated with  termites,  270 

Pseudo-leadership,   197 


Oesting,  R.  B.,  92 
Overcrowding,    31,    50;    effect 

on  growth,  91,  103 
Oxytricha,  77 


Quintuplets,  Dionne,  201,  207 

Retzlaff,  Elmer,   102 
Robertson,  T.  B.,  75 


INDEX 


293 


Schjelderup-Ebbe,     T.,      176, 

184,  185,  189,  191 

Science  in  general,  15,  20,  90 

Selection,    120,    125,   210,   228 

Sex,   47;    origin,    84;    relation 

to    social    dominance,    191, 

194;  division  of  labor,  247, 

251 

Shaftesbury,  third  Earl  of,  24 

Shaw,  Gretchen,  92 
Shoemaker,   H.   H.,    185,    191, 

193 
Social,   origins,    29,    244,    272, 
274;    inertia,  43,  44;   appe- 
tite, 44,  47;  facilitation,  134, 
172;  hierarchy,  175,  207 
Sociology,  general,  200 
Spermatozoa,  mass  protection, 

68;  length  of  life,  83 
Springbok,  108 
Starfish,  brittle,  44 
Statistical  probability,  54 
Struggle  for  existence,  26,  51, 

210,  242 
Sully,  236 

Survival  value,  32,  49,  133, 
173,  244;  of  breeding  col- 
ony, 111;  of  social  hier- 
archy, 207 

Tadpoles,  effect  of  numbers 
on  regeneration,  98 


Temperature,  mass  protec- 
tion from,  58;  effect  on 
growth  of  mice,  102 

Termites,  32,  48,  261,  264, 
265,  271 

Territory,  bird,  135;  a  factor 
in  social  rank,  193 

Toleration,  43,  44 

Trial-and-error,  44 

Tropism,  246.  {See  Forced 
movements) 

Tsetse  fly,  minimal  popula- 
tion, 108 

Ultra-violet,    mass    protection 

from,  59 
Undercrowding,    50;    harmful 

effects,  52;  effect  on  growth, 

91 

Vetulani,  T.,  99 

War,  210 

Wasps,  262,  264,  265;  solitary, 
46;   importance  of  females, 

259 
Welty,  J.  C,  92,  136,  159 
Wheeler,  W.  M:,  29,  40,  246, 

259,  262,  264 
Wheeling  of  bird  flocks,    198 
Wilder,  Janet,  59 
World  Court,  238 
Wright,  Sewall,  117,  240